Fingering and Practice
The C major chord shape is similar to the G chord in that you're using the same fingers on the same frets. The only difference is what strings they are on.
Start with your G chord position. Now as if your index and middle fingers were glued together, lift them off of the 1st and 2nd strings and move them up to the 2nd and 3rd strings. Your new position will be index on the 2nd fret, 3rd string and middle finger on the 3rd fret, 2nd string. Play each string to make sure that all notes are coming through clearly, then play along with the tab.
The C Major Chord
The tab below will give you an aural reference to play along with. Go slowly and make sure all of your notes are coming through clearly.