F1 hybrids (filial hybrids to be precise!) are seeds which are genetically identical, eg if you have, say F1 sweetcorn seeds, they will all be genetically identical to produce cobs at the same time.
usually they are made to produce uniform plants eg of the same colour, or for disease resistance.
they can cost more (the "parent" plants are often hand pollinated, and have various bits removed to prevent them naturally pollinating - which all adds up) but you should get a good plant from htem.
if the F1s go to seed, their offspring plants will not be "true", ie like the F1s were.