Hi,
here is a couple of examples:
Past – John worked for XYZ company two years ago after he got married.
(he no longer works for this company)
Present perfect- John has worked for XYZ company since he got married.
(he started working there after he got married, and he still is up to now)
Rule of thumb: if you just want to simple express an idea or describe something that happened in the past, [past] tense is sufficient.
If you just want to express an idea or describe something that started sometime in the past but it’s on-going, then use present perfect.
I lived in Hong Kong for a few months while I was doing a project two years ago. –done and past.
I have lived or [been living] in Hong Kong for 3 months now and probably longer until the project it’s completed. (here, I have included present perfect progress as an option which I prefer).
Hope it helps...