F

In C, your ring finger is on the fifth string, third fret, middle finger on the fourth string, second fret, your index finger on the second string, first fret. To get to F, leave your index finger where it is, and move the other two fingers toward the floor as you hold your guitar, until your ring finger is on the fourth string, third fret, and your middle finger is on the third string, second fret.

Practice making this two-finger change a few times, or a dozen times, leaving your index finger on the second string, first fret all the while. That finger is common to both C and F shapes. Do it over and over until you begin to get more comfortable with it.

Here comes the hard part. With your fretting hand in our F position, you must somehow, lay your index finger flat to cover both the first and second strings at the first fret. Impossible? Just difficult. 

Here's another approach to making the chord form F. Take your fretting hand off the guitar altogether, and start again. Begin by pinching the neck of your guitar between your thumb and index finger. Your thumb ought to be somewhere on the back of the neck where the first fret would be if the first fret were on the back of the neck. Now your index finger ought to be able to lay flat across the first and second strings at the first fret. You won't need to squeeze too hard, just get your hand in that position and inspect it. There ought to be a lot of space between the palm of your fretting hand the the back of the neck of your guitar. 

Also, see if you can keep the two joints closest to the tip of your index finger straight as it lays across the first and second strings. Those two joints may bend a little as you make the long reach to the fourth string, third fret with your ring finger. Add your middle finger to the third string, second fret. When you are satisfied that you've done everything you can to get your hand in this difficult chord position, take it off and do it again. And again.

Next, it's time to F from some of our other chords. C and G are good ones to begin with. Make up some exercises like the ones we've used before and hang in there. Some find F to be really tough. When you add your strum, begin strumming F from the fourth string.

Two or more strings held down with one finger of your fretting hand is called a barre, or in our case, a half-barre. A full barre usually refers to holding down all six strings with one finger, as when making barre chords. We'll get to those later. 

I've seen beginning students make this F shape, complete with half-barre, on the first or second try and able to get all four strings to sound clearly. It's not common, but it's not uncommon either. 

Making the chord form F, and changing smoothly from chord form to chord form is again, an issue of finger strength and coordination. So far we've become acquainted with D, A7, G, C & F. If you're not happy with the speed and accuracy of your chord changes, or some of your strings are muffled or buzzing when you strum, think about the letter P. As in Practice.