How to approach sheet music as a beginner
While sheet music can appear to be opaque and unreadable, it isn't as complicated as it seems. Additionally, you do not need to read music well to begin getting value from it. Simply being able to decode the notes is hugely freeing. Over time this develops into a more natural fluency.
Like written English sheet music is organized into lines but unlike a spoken language these do not contain words. Each line of music is represented by 5 more lines like below. These 5 lines are collectively called the 'staff' or 'stave'. Each line or space within this represents a different note, with higher lines representing higher notes. Circling a given line tells you to play that note on your instrument, and are read left to right.
Perhaps confusingly, these circles are also called 'notes'. They come in different shapes as in the following example. Notice how all of them still feature a round 'head'. Only the head determines the pitch represented by the note, the differences in shape describe rhythm. Thus, these all represent the same note:
Initially, I think it is easiest to focus on learning the notes, and learn rhythms by ear. As each of the lines within the staff represents a different note, learning to read the notes is just a matter of associating these with notes on your instrument. There are at least two different ways of approaching this, subconscious association and learning the names.
The goal of subconscious association is to develop a direct connection between the notes that you see, and their fingerings and durations. An analogy can be found in reading, when you are fluent in a language, you do not sound out words a letter at a time, but rather associate the sight of the word with the sound. It just 'pronounces itself' in your mind the instant you see it.
Learning using this technique begins with sheet music within a very narrow range, using possibly only two or three notes. It is simple enough that you are able to consciously connect what you see with the fingerings, and play it. This gradually becomes subconscious, and you slowly add more notes and their fingerings over time.
The next example shows a piece of music that you may start with using this technique. If you reference the example which shows the notes of different positions, you can see that the notes used are F, G, and A. You can then look them up in a fingering chart. You'd then relate the notes you see to your instrument's fingerings. Once you start to get it, you'd reinforce that by playing more exercises in the same range.
It should be apparent that this approach really requires crafted exercises, and it is much easier if the same music is also available as audio or you work with a teacher who can play it for you.
Learning the names
Learning the names on the other hand starts in the analytical mind. You first learn a few rules, such that the note G is on the second line from the bottom, or that the spaces spell the word 'face'. From this point, you can begin to 'decode' notes from the music, and over time you learn which positions correspond to which note letters at sight. Eventually, this falls away, and you go directly from the sight of notes to their fingerings.
As this is quite arduous before you memorise the notes corresponding to various positions, due to the need to count from reference points, it can help to transcribe to an intermediate notation. ABC notation is convenient, as notes are represented using the letters of the alphabet. Notes from C below the 5 line staff are notated in upper case, and the next octave continues in lower case.
C D E F G A B c d e f
Using an intermediate notation like this, you can go from the sheet music to intermediate. Then you can break it down into sections a few notes long and practise the fingerings repeatedly until it gets into muscle memory. As you do this more, you start to connect the positions in sheet music directly to fingerings.
Which is better?
Both of these approaches have pros and cons. Subconscious association is good because it allows you to develop a direct connection between notes and fingerings, which is essential for sight reading. However, it can be boring as it forces you to start out with trivial music. Beginning with note names allows you to start working on complex music from the start, but developing the direct association may take a lot longer. The transition may actually be jarring when you notice that you stop thinking about all of the note letters.
My recommendation is to try both and see which method works better for you. Using the direct association technique you'll still want to learn the names for different positions, as it allows you to communicate with other musicians. Being able to separate the notes that you see from the fingerings they represent is also very useful on the ocarina. It allows you to read onto ocarinas in different keys, at the written pitch. See 'Playing ocarinas in different keys'.
Developing your skill
As the goal of this page is to give an overview of approaching sheet music as a beginner, there are many details that I have left out. There is no need to get scared off as they extend naturally from what you have learned. Clefs for example define which note is on which line. Also, in its most basic sense sheet music is designed to represent the natural notes, scales such as C Major and A Minor. Other scales are notated using sharps, flats and key signatures. There are many websites and books covering these topics.
It is worth being aware that when one approaches sheet music as a beginner there is a tendency to think one note at a time, because everything is a conscious effort and hard at first. You should aim to progress beyond this stage to thinking about groups of notes called phrases. Playing one note at a time is a large part of the 'beginner sound'. It tends towards uninteresting performance as you just hear one note after another without emphasis or structure.
Sheet music can present music in a very plain and immutable way. Working from it alone can obscure the options of improvisation. There are also many subtle details which exist in human performances that sheet music cannot represent. Due to these factors it is very important to listen to human performances as you learn to read sheet music. Find multiple renditions of the same thing, and pay attention to the differences.
Doing this comes very naturally with rhythms, which is why I advise learning rhythms by ear. As you listen to performances, clap along with the notes of the melody. This also leads naturally into reading rhythms from sheet music, as when you look at the notation while hearing the associated rhythm, your mind will connect them. See: 'Reading rhythms: forget counting'.
As your skill continues to improve you'll stop thinking about the individual notes and instead look at the shapes that they form or the spaces (intervals) between them. For example, the following shows two instances of a common pattern; play a note, play the note above, then play the starting note again. First from G, then again from high D. As you progress you will be able to play such patterns without caring about the named value of a higher note. You just ascend to the next note in the scale, then drop back down again.
Overall, don't get discouraged and keep working on it. It does get easier over time.