You "give someone credit" when you name them and say they have done something important. A line underneath a photo saying "Photo by Annie Leibowitz" is a "photo credit" that names the photographer who took it. The long scrolling list at the end of a movie is "the credits:" Gordon Willis was director of photography, Warren Clymer was the art director, and so forth. A good boss, talking about a successful project, will "give credit" to the people on the team who made it successful: "We had good teamwork, but I want to give special credit to Rachel for coming up with the key idea that made the project successful."
You can say "I give myself credit" when you are praising yourself. You would do it to call attention to something you think is a fact, and not just an empty brag. "We had good luck on our trip, but, to give myself credit, it wasn't all luck--I did spend a lot of time planning it."