It can be even simpler with intervals: 1 is a half-tone, 2 is a whole tone

Major scale: 2 2 1 2 2 2 1 Minor scale: 2 1 2 2 1 2 2 etc

They sum up to 12 (octave)

Now that you got the theory, practice playing them evenly from every note and make sure they sound right.

Fingerings are a separate story though.