Some help on- SOME F2L cases and Others

[noobcuber]

Hi
I am currently getting sub 40 solves every second solve or so

my F2L takes 20 seconds so I am worried because what takes the most time is when say if you solved the white cross first.

I have the case where the white is to the left of the corner if you have it on hte right of the F face and I put the edge one move to the left from the corner then I perform F' U' F

but sometimes it pairs up the wrong way what could I do differently in this case??
aLSO

i HAVE RESearched comutators and need to learn them but I just dont see what they are for or when and how you use them??

 

[LamentConfiguration]

I'm sure there is an algorithm for that specific case on one of the many F2L sites.

http://www.cubestation.co.uk/cs2/index.php?page=3x3x3/cfop/f2l/f2l

 

[Crzyazn]

Im assuming you're using intuitive F2L...

If you're really having trouble, it isn't heresy to go take a look at the algorithms to help you along.

http://www.cubewhiz.com/f2l.html

good ones with some good explanations

 

[Lucas Garron]

I think you need U' R U2' R' U2 R U' R'.