Two ways of playing F using the left hand thumb.
In the first example the open A string can be played as part of the chord but
tends to make the sound a bit 'muddy' so is usually left out.
Try moving the shape up to the 5th fret however and the open A gives you a big doubled up sound on the bottom of an A chord.
The second example shows a full 6 string moveable shape - just like a barre chord.
Try to get your 1st finger across the top 3 strings ( as indicated in the diagram ) as this allows for the minor version of the chord as well and so is a good habit to adopt.
If you find this difficult then just get the top 2 strings for now.
Any new technique can feel a bit difficult at first and so you may well think — I can already play F so why bother.
- The reasons are; firstly flexibility , I also use normal barre chords a lot but there are some things possible with this way of playing that aren't with a barre, and secondly comfort - I just find it more relaxed playing something like the example on the soundfile using this fingering - also if you've got a lot of barre chords to play switching to this shape every so often gives your muscles a rest!