Build a Major chord
Any two adjacent notes moving clockwise around the circle are a perfect fifth (seven semitones). If you start from the first, count four more clockwise around the circle, this is the note between them.
For example, F -> count 4 from F (F C G D A) so A goes between them (F A C) for the major chord. It gets confusing at the bottom of the circle, but if you work through it you will find it still works.
For example C# F Ab (C# E# G#).
**Note:You must take the notes that are the same into account: C#/Db, Gb/F#, Cb/B. The progression through this part of the circle is a compressed B F C G D so the fifth progresses to the next note past the duplicates.
For example Bmaj is B Eb F# (B D# F#). The progression around the bottom of the circle is either E B F# C# Ab or E Cb Gb Db Ab which are the same. Alternately, you can convert the flats to sharps and keep the pattern of F A C E and E G B D F (spaces & lines in treble clef) -- B D# F#, F# A# C#, Eb G Bb, Ab C Eb, E G# B for your major triads. Make sense? Work through it once and it’s easy from then on. :-)
Hope this helps! Practice hard and let me know if you have any questions!