In the beginning

Now we know intervals we can find the notes in a major scale by working them out from a given 'tonic'
First a few simple rules
1 - the letters that represent each degree [each note] of the scale can only be used once
there can only be one A, one B, one C, one D, one E, one F, one G

2 - they will always occur in alphabetical order until you get to 'G' [where the following note is 'A']

3 - You will also need to know the notes of the chromatic scale so here there are. Use them for reference:
A, A#/Bb, C, C#/Db, D, D#/Eb, E, F, F#/Gb, G, G#/Ab, A, and so on
Note that A# and Bb are the some pitch [as in the same key on a piano or same string and fret number on a guitar] but they are not the same note. They are mealy two different names for the same pitch.
Also, you need to know the spelling of a major scale.
The 'spelling' is simply the list of intervals with respect to the tonic.
The major scale is spelt as shown below:
Tonic [where you start from]
Major 2nd [2 frets up]
Major 3rd [4 frets up]
Perfect 4th [5 frets up]
Perfect 5th [7 frets up]
Major 6th [9 frets up]
Major 7th 11 frets up]
Octave [12 frets up]

When the Tonic = C the notes of the scale will be C, D, E, F, G, A, B
Next you need to figure out if the notes are flat [b], natural, or sharp [#]
To do this you use the spelling of the scale, your knowledge of intervals and the list of chromatic notes.
The 2nd note is a major 2nd interval above C [1 tone or 2 frets above the tonic]
Two semi-tones above C [found by looking at the chromatic scale] is D
'C' is the starting point
one semi-tone up is 'C#/Db'
another semi-tone up is 'D'

The 3rd note is a major 3rd interval above C [2 tones or 4 frets above the tonic]
Two tones above C [found by looking at the chromatic scale] is E
'C' is the starting point
one semi-tone up is 'C#/Db'
another semi-tone up is 'D'
the next is 'D#/Eb'
and the next is E

if you follow this through to end, looking at all intervals of the major scale where C is the tonic
you will end up with C, D, E, F, G, A, B, C

Lets look at a major scale where E is the tonic - the scale of E major
When the Tonic = E the order of the notes of this scale will be E, F, G, A, B, C, D and E
but we do not yet know if there are any # or b notes. We need to work them out as we did for C major [above]

The 2nd note is F 'something' and is a major 2nd interval above the E [1 tone or 2 frets above the tonic]
'E' is the starting point
one semi-tone up is 'F'
another semi-tone up is 'F#/Gb' - which do you choose? F# or Gb?
Remember that all the notes have to be in alphabetical order and occur only once
F comes after E so you choose the F#

The 3rd note is G 'something' and is a major 3rd interval above the E [2 tones or 4 frets above the tonic]
'E' is the starting point
one semi-tone up is 'F'
another semi-tone up is 'F#/Gb' - which do you choose? F# or Gb?
The next is G
And the next is G#/Ab
We already have E, F#, and we are looking for G something and have G#/Ab to choose from
So it has to be G#
Try to work out the rest of the scale for yourself
If you get stuck that's ok. Shout and I can show you where you are going wrong and why.
It's much better that you start figuring this out yourself and me nudging you in the right direction rather than me spoon feeding you list after list of scales and you never understanding why
If you think you have the hang of it, try working out the notes in 'F major' and 'A major'
Don't worry about getting it wrong
It's all part of the learning process

--
--
Frank