Hey man! It's great that you're looking to learn the notes on the neck. It may seem like a daunting task - however it's easy & simple. I've attached a sheet I use with my students in order to get them to visualise the system.
Let me take you step by step:
1. I like to think of the notes on the neck being called the Musical Alphabet - i.e the letters of the language used to make all of the music you hear. There are (technically)
only 12 notes, which is lucky for us!
2. The Musical Alphabet starts at
A - like our normal alphabet - but instead of going to Z, it stops at G#. It also has some extra features (Sharps & flats)
3. The Musical Alphabet is made
entirely of 'Semitones' - this is a fancy musical term for
'1 fret' on the guitar. So each letter you go up in the Alphabet, you go up 1 fret each time on the guitar.
4. Before we continue, let's demistify what a Sharp (#) and a Flat (b) are, as they both exist in the Muso Alph. They are basically instructions that tell you that a note has RISEN or FALLEN by a semitone.
Example: If we are on A, and we want to 'sharpen' it - we would go up (to the right) 1 fret/semitone. This note would now be called A#, because it's one above the A, you've just sharpened the A note. The same goes for Flattening a note. If you go 1 fret left of A, you get Ab, as you have flattened the original A note.
I good analogy is that if you sit on a 'sharp' pin you jump UP, and if your Car tire goes 'flat' it sinks DOWN.
Sharp means up, Flat means down etc.
5. Grab your Guitar as you read this and pluck the open 'A string'. The second you pluck that A string, you're dropping yourself at the start of the Musical Alphabet on my sheet I've attached.
6. So we're at A on the Musical alphabet, and say we want to sharpen that A to make it A# - we go from fret 0 (open A string) to fret 1, which we could name A#. If you keep rising up the frets you rise up the alphabet, A, A#, B, C, C#, D, D#, E, F, F#, G, G# - you'll find there are more frets after this -
the alphabet just reverts back to the beginning.
7. You might be wondering right now where all the flats are? This is the only part of the alphabet that is a bit strange - So we mentioned that Going up 1 fret from A makes A# (which would take you to 1st fret on the A string) - but what if we landed on B and flattened it? - It would be called Bb - which is also 1st fret on the A string. So basically,
any Sharp note has an equivalent Flat note, depending on how you view the note.
A# & Bb are essentially the exact same note and will produce the same sound on the fretboard, the same with D# & Eb, G# & Ab etc.
8. If you look again at point 5, you'll see that there is no B# or E#. This is because
B & C are stuck together, and because E&F are stuck together. Think of them as the two couples of the Alphabet. If they're stuck together in the Alphabet, then they will
always be stuck together on your fretboard.
9. So you can use all the information above to find all the notes on the A string. What about every other string? Here's the good news: Your open strings on the Guitar are access points straight into their note in the Alphabet. So if you take the low E string, 1st fret would be F (because they are stuck together) and if you went 1st fret B, you'd go to C and so on. Your entire guitar is just this 12 note system repeating & repeating endlessly.
10. Now that you know how it works - here's a tip for getting to the point where you know it off by heart when looking at the fretboard: Take a string a day and
practice finding all the Natural Notes (I.e all the notes that aren't flats/sharps). You'll eventually start to see patterns of 2 frets & 1 frets come into view, as the 2 fret distance between notes will mean you're skipping over a sharp/flat and the 1 fret distance will mean you've found the alphabet couples (B &C or E& F) - When I say 2 fret distance I'm counting the note you're departing from (G to A, with G#/Ab in the middle etc)
11. Pretty soon you'll look at 1st fret low E and your brain will just say 'F' and you'll start to have a more vivid view of the notes on your fretboard
Hope this clears some things up & don't hesitate to DM if I've missed anything!