As Phil pointed out Rui the size shaft on your bits will depend on your router. In North America many Ryobi routers only accept 1/4" shaft bits (about 6.35mm) but I can't say for sure that is what you have there. Your instruction manual should say. The most common bits that are used are round overs between 3/16 and 3/8 radius, straight bits for cutting grooves and recesses, roman ogee bits for edge treatments are popular, and maybe a cove bit or two in the same sizes as the round overs. If you want to make signs then a v point bit or a sign making bit (v with the tip cut off) would be needed.Those bits would get you started.
Someone I consider a master woodworker once told me that a master woodworker is not someone who never makes mistakes. He is someone who is able to cover them up so that no one can tell.