I get you want to help.
Does get in this context mean “know”? Or “understand”?
In this case, “get” means to understand something said (or hinted) by someone else.
Normally, “get” means to receive something from another person: “I got your letter” means “I received the letter that you gave me.
Therefore, the sentence “I get you want to help” means “I received the information that you told (or implied to) me, which is that you want to help.”