every time I want to go on that, i don't know what needs to go in there. can anyone help me?

Your database username plus your database username password

You need to create a database and username add permisions.
Please search the forum you will find what you need.

I did that but it still wont let me in.

For User Name, you have to write: yourwebsitename_username

Ex:
My website wordpress name is: mummies
And I made a username for my database wordpress as fraser
So it should be: mummies_fraser

So when I log into the phyadmin, I use:
User Name: mummies_fraser
Password: whateverpasswordicreated

And "yourwebsitename_username" must be 16 characters long, including the underscore (_)
So with my example above, mummies_fraser is 14 characters long.

Hope that helps.