A scale is a set of notes played in order up or down. The major scale is the bright, happy-sounding "do re mi fa so la ti do". Every major scale uses the same pattern of steps: whole, whole, half, whole, whole, whole, half.
Start on C and that pattern lands on all white keys: C D E F G A B C, because the half steps fall on E to F and B to C. Start on any other note and you'll need black keys to keep the pattern. G major needs one: F♯. F major needs B♭. D major needs F♯ and C♯.
Eight notes don't fit under five fingers, so the right hand plays C D E with fingers 1 2 3, then tucks the thumb under to play F, and carries on with 2 3 4 5 to the top C. Keep the hand still and let the thumb travel under it.
Practice
C major
C major with the right hand, from middle C. Watch the fingers: the thumb tucks under for F.
AC4SDDEFFGGHAJBKC5LD;E'FGABC6WETYUOP
Computer keys: ASD… for the white keys, WET… for the black keys, ZX move an octave.
More info
Tips
Play each scale slowly with a steady count, a little louder on every C (or G, F, D). Smooth thumb crossings come before speed.
Playing the exercises
Use a MIDI keyboard (Chrome, Edge, Firefox or Opera), the computer keys (ASD… for white keys, WET… for black keys, ZX to move an octave), or tap the keys on the screen. A key lights up after a couple of wrong tries.
The answers
What is the pattern of steps in a major scale? Whole, whole, half, whole, whole, whole, half. W W H W W W H. From C it gives all white keys, because E to F and B to C are the half steps.
Which black key does G major use? F♯. Following the pattern from G, the seventh note has to be a half step below G: F♯.
Which black key does F major use? B♭. From F, the fourth note has to be a half step above A, which is B♭.
In the right hand's C major scale, which finger plays F? The thumb, tucked under. After C D E with 1 2 3, the thumb passes under to play F, then 2 3 4 5 finish the scale.