What is Penetration Testing
It is a type of testing focused on security. You assume the role of an attacker and try to compromise a system.
Types of Penetration Testing
Whitebox - we can easily obtain all the information we need. The target system is cooperative.
Graybox - we have few information that the target system is willing to give. The target system is reluctant.
Blackbox - start from scratch. No information is being given voluntarily by the target system. The target system is indifferent.
Always check your local laws on what is legal to do. You usually need explicit permission to test a system.