i already have one database, but i need another one for another program. can i open another database? and how? thanks!

Could you be a little more specific please.

i already careated one database for a website. now i have another website needs a database, but in phpmyadmin i can't create another one...

The whole concept of a database is that everything is stored once.

One database can have hundreds of users. Each user can have hundreds of tables and those tables can have the same names as tables belonging to other users.

Unless you are storing billions of huge records in your database and have blown the capacity of the database system (and I have never seen a company with enough data to even come close) then there is no requirement for a second database.