Username and email for minecraft?

So I was making a minecraft account but forgot i needed to buy the game so i canceled it and I was logged in so i went back to the website and realized i was logged out and i try logging in and i realized it said username so i try putting the one i want it and it didn't work so i put my email address and it worked but when i buy the game will my username be my email or can i still make a username?

If you buy the game on mojang, you wil be able tp make a username when you have bought the game. But you wil have to login with your email.
Hope i helped.