The C7sus4 chord (shortened C7sus or Csus7) is a sus4 chord with a minor 7th. The easiest way to get the minor 7th on the guitar is to take a Csus4 chord, find a second root C on the higher strings and move it 2 frets (a whole-step) downwards to the minor 7th Bb.
Thus in a C7sus4 the minor 7th is the tone Bb, so a C7sus4 consists of the tones C (1), F (4), G (5) and Bb (7)
The C7sus4 is often used as a replacement chord for C7 (dominant 7th chord). But since the C7sus4 chord has a strong tendency to resolve back to C7, you may play C7sus4 in the first half of a bar and then go back to C7 instead of replacing a whole bar of C7. You can also go back and forth between C7sus4 and C7 several times.