The F chord on the guitar is one of the toughest chords for beginners to learn. But do not fret (see what I did there?). With enough practice, this chord will be as easy to play as that E minor chord you learned.
Here is the basic version of the F chord. It is played by barring the first two strings with the first finger on the first fret, then picking up the A note with the second finger on the second fret of the 3rd string, and grabbing the F note with the third finger on the third fret of hte 4th string..
Here is the barred version of the F chord that gives you a more full, fat sound. This chord is played by barring the first fret with your first finger, then placing your pinkey and ring finger on the 4th and 5th strings on the 3rd fret, then placing your second finger on the 3rd string second fret.
Try this version for a lighter sound. This one is played on the 8th fret by barring string 1 through 5 with your first finger then barring the 2nd, 3rd, and 4th with your ring finger. The chord diagram here has you using fingers 2,3,4 for the 10th fret notes. Try it both ways and see what is more comfortable.
There, now you know three version of the F chord on guitar. Practice switching from C to F and F to C. Then try switching from G to D to F to C. See if you can tell which Led Zepellin song that is!