Credit has several meanings. "Give me a little credit" is a casual phrase whose meaning I cannot explain concisely. You would say it in response to someone suggesting that you may have done something without thinking. "Did you call the right number?" "Give me a little credit: I called the number twice before." Credit is also a phrase used often in financial terms. A credit card is a card which allows one to spend money in advance of earning it. The bank extends a "credit" on the assumption that you will pay it back in a timely fashion. Credits like Italki credits are a similar concept: the user has purchased the credits, meaning they have already entrusted the money to Italki and, in return, Italki distributes them at the appropriate times. Hopefully, that was of some use.