Present Perfect: "I have written this essay." Present Perfect Progressive (continuous): "I have been writing this essay."

I am sure the grammar books have better explanations than mine but this is how I understand it: the present perfect simple is used to emphasise the result of the activity e.g. I have studied English for 10 years (and now I speak English well) The present perfect continuous is used to emphasise the activity itself e.g. I have been studying English for 10 years (and it has been really hard work)

Present perfect emphasises the result of an activity. Present perfect continues emphasises the duration of activity , but it doesn't mean that an action is completed I have been working for a publisher at this company for 5 years. Means that you have worked at this company for 5 years and still working at it. but I have worked here for 5 years . Means that you have worked here for five years and don't work here anymore.