pluggin development help (pluggin should create a table in DB )

Hello All Masters,

I am developing a pluggin , i am just a beginner. I want my pluggin to create a table in database on click of a button ( which is in pluggin).
So how do I get the database credentials ..like database name hostname , username and password.
I know I have to add_action and let user enter the details before using pluggin. Please tell me how to achieve that.
Please.