If you have one sharp it will always be an F. The order of sharps, and flats will always be the same when looking at key signatures. Just like the outside circle, the minor key signatures change by going up, or down a perfect fifth (A - E - B - F#). The relative minor of C is A, so they are both on the top. The smaller circle on the inside represents the minor key signatures.

Since G-flat major, and F# major have the same pitches, and are just enharmonic (different names for the same pitch) spellings of each other they are on the same spot.

There can only be a total of seven sharps, or flats in a key signature. F major has one flat, B-flat major has two, etc. If we move counter clockwise around the circle starting at the top each letter moves down a perfect fifth, and one flat is added. G major has one sharp, D major has two, etc. As you move clockwise around the circle each letter moves up by a perfect fifth, and one sharp is added to the key signature. This letter refers to the key of C major. C is the top of the circle of fifths, C is the note directly between bass and treble clef, C is on the middle line in alto clef, and much more.

You can usually think of C as the middle of most everything in music.

What is the order of sharps and flats