This lesson is about scales. Its basically the same for all instruments, but im gonna take the piano as example this time.

This is the scale of C major. And yeah, its that simple.
To make it even more simple, they've given each note a number:
C 1
D 2
E 3
F 4
G 5
A 6
B 7
C 8 (the next C on your keyboard)
Now here's where it gets confusing for a lot of people. If you look at the black keys, you might notice that between E and F (and B and C) there's no black key. And this kinda messes things up when you wanna play any of the other major scales. For example the G major scale which consists of: G A B C D E F#. Now where did that F# suddenly came from?? Well its not as hard as it seems, its actually quite logical.

The picture above shows the C major scale and as you can see, there's 2 parts of the pie between C and D, but only 1 between E and F. This goes for any major scale. If you look at the sequence for C major, its C then 2 parts further brings us to D, another 2 parts and we're at E, then 1 part to F, 2 parts to G, A and B and 1 part back to C. So the sequence of the major scale is 2, 2, 1, 2, 2, 2, 1.
Now if we do the same for the G major scale, then you get this:
You start with the G, from the G key you count 2 keys, so thats G# and then A.
From the A you count 2 keys again, so thats A# and then B.
From B you count 1 key, so thats C.
And so on.
If you did this right, you should have G, A, B, C, D, E, F# and G, coz from the E you had to count 2 steps, so thats F and then F#. Got it?
1 G
2 A
3 B
4 C
5 D
6 E
7 F#
8 G
Now you try and do the same for D, A, E and B major