mature apple trees

I just moved in and there are about 30 apple trees in the yard I do not know what type they are. I just need to know if there is any thing I can do to the tree's and get good apples from them. I do not know anything about this subject

 

http://web1.msue.msu.edu/fruit/

 

Thank you for the info. I think this will help me. I will ask more question I am sure.

Thanks again,

Lindamae