F1 generation are the offspring of Parental (P) generation. They are the hybrids of parents. They will have either hybrid phenotype or only the dominant phenotype of one of the parent.
F2 generation are the offsprings of F1 generation when they are allowed to cross or mate. Some of the offsprings in F2 generation will have phenotypes from both parents of P generation i.e. dominant or recessive as well as from F1 generation