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.