"To take credit for something" means to accept honor for an achievement. The implication is that the honor is not deserved. Someone might take credit for inventing the Internet, for example.

thanks Lisa

Sth is shorthand for 'something'. When you take credit for something, you ask or receive acknowledgment for your work. Basically, you are asking someone to recognize your work/deed. Ex: I better get credit for my paper even though the teacher said she would not accept late work.