Al, the fourth is ALWAYS directly to the left of the root note on the circle. In the key of C, you shift to F. F is the subdominant. The dominant is always the fifth which would be G in the key of C.

The notes in a scale are designated:

1. Tonic
2. Supertonic
3. Mediant
4. Subdominant
5. Dominant
6. Submediant
7. Subtonic or Leading tone

These designations are not all that important to know. What's important is to know the musical distance each note is from the tonic or root because that makes all the difference. In adominant 7th scale, for example, the 7th is flatted. That doesn't mean the 7th has to have a flat sign in front of it; it means that the 7th is 10 half-steps away from the tonic instead of 11 as it would be in the major scale. The difference sounds insignificant but it is huge. Songs in dominant 7th sound dark, sinister, mean. Song in major 7th sound sugary, sweet, light.

The secret to writing bubblegum rock songs was to make them major 7th so that they sounded sweet and non-threatening. True rock sounds are generally in dominant 7th or in minor scales (flatted 3rd and 7th) and so have that "heavy" sound.