DOMAIN – HOSTING

Our question is this – when having a blog in word-press and are asked to get a domain, does that mean that we have to buy the domain from word-press in order to keep our content existing in our blog and host it somewhere – OR, word-press itself has already given us a domain when having our blog which we just need to host it somewhere ???

In other words, when having a blog at word-press does it mean we already have a domain for it OR do we have to buy it FROM word-press and host it anywhere we like???