Few friends and a few friends have almost the same meaning...that there are not many friends..but "a few friends" have a more positive meaning rather than "few friends": Few -means that you have a necessity to have more...there is a lack of smth. A few-means that you have some and pretty satisfied with it. E.g. I have few friends(=I am almost alone) I have a few friends (=and I am glad that I have them) I have little water in my cup (=it is not enough for me) I have a little water in my cup (=at least I have some...and it will be quite enough for me for this time)

Both mean "small number of friends." Both sentences are grammatically correct. I get the same information from both sentences, but there is a small difference. "Few friends" emphasizes how small the amount of friends is. "A few friends" refers to the friends you do have.