It means deserving blame, so one example of it in a sentence would be: He saw the crime and did nothing to stop it, so he is just as culpable as the one who did it. A second example is, They are...
Use it's (with the apostrophe) only when you mean "it is" or "it has." For example: It's time to go. (It is time to go.)It's been a long time. (It has been a long time.) Use its (without the...