Contacts is central place for all clients. You have to open contact first, because you can use this contact for opening customer or/and vendors. When you open customer and vendors from the one place, you will get relation between them. This relation is important for the future work.
You can to use customers and contact independently, but it requires specific configuration in Marketing Setup. Do not do it by yourself without a your partner.
I'm not sure what license you have, but you can use contacts except for the customer creation, for many different reasons; you have complete CRM module (if you use Extended Pack license).
If you have contact as Person Type, you cannot create Customer from it.