Hi,
i'm not very clear what the diferrence is between :
- I have just done it
- I just did it
txs a lot
The difference is very minimal.
'I have just done it' is present perfect tense. In this scenario the thing you have done has a relation to the present. When the particular task is completed is not mentioned in this case.
'I just did it' is simple past tense. It could give a hint to the time you finished the task, eg, 'I just did it a an hour ago'