For example: "I have sat on this spot. I have been sitting on this spot for over an hour." First one means you have already completed action by now. The action is complete currently. The second one means that you have completed the action and are still continuing this action. the action is currently complete but is continuing right now. Apart from that, I know nothing else to say.

Thank you very much for your explanation. :) (Talking with strangers? Really? What's a unbelievably stupid idea)

With the present perfect continuous, the action began in the past and continues to the present moment. Justyna, have you washed the dishes? No, mother, I haven’t. [No result] I have been doing my homework since I got home [Explanation]. Here you are saying that you started your homework the moment you arrived home, and you are still working on it (the entire time from arrival home to the present moment). Another example: How long has William been working at the zoo? He’s been working there since 2015. [i.e. He began in 2015, and his work continues from 2015 to the present].

With the present perfect, we are talking about an action in the past with a result in the present moment. We don’t know when the action happened (and we probably don’t care). We are interested in the result of the action (or whether or not the action ever actually happened). Mother, may I have some flaki z olejem? That depends, Justyna, have you done your homework yet? [Mother wants a desired result before giving you flaki z olejem.] Yes, I have. I have done my homework. [Yes, the action did happen. It is completed.] Alright, Justyna, you can have some flaki! Another example: I’ve done my homework. Now I have time to log on to italki and talk to strangers from the internet.

You did any work or action before some time Exp. you are seating on a chair and having tea. Your mother calls you " Justyna have you taken tea" and same time you reply " No I am taking my tea" (This is present tense). After some time you tell your mother that " I have taken tea" means you have completed the action or work that you were doing before some time. This perrsent perfect tense. Present perfect continuous tense- you started any work in past time and still you are doing this. Exp- you joined a company before a year ago and still working there. You will say " I have been working in xyz company for one year. If you mention the date of joining in this sentence You will say " I have been working in xyz company since ( date of joining) 4 April 2018.