What is the difference between the present perfect tense and the past simple tense?

I hope you will understand through this example 

Present Perfect Tense : She has done it .

Past Simple Tense : She did it .

I hope I was of some help

Thanks 

You use the simple past to talk about an event that happened at a certain time.

Ex.: I went to UK two years ago.

The present perfect tense is used to show a past event at an uncertain time.

Ex. I have gone to UK.

The present perfect tense is used to describe an event in the past. The word 'present' is used in the tense to show the present effect of a past event.

An easy way to remember:

Focus on adverbs like yesterday, ago and last night that go with simple past tense.

Adverbs like already, since and for go with present perfect tense.