As a non-native speaker I think they're one of the easiest things to write correctly. I don't get the confusion. With what I really struggle is the tenses. I'll never understand the diference between 'I did somethng' and 'I have done something'.
They are 2 different tenses, there are 3 tenses past, present, and future (if you wanna get really technical, there are only 2 tenses with verbs). Everyone know that for the most part. They can however be broken down even further, simple, progressive/continuous, perfect simple, and perfect progressive/continuous. Using your example:
Past simple: I did
Past progressive/continuous: I was doing
Past perfect simple: I had done
Past perfect progressive/continuous: I had been doing
Present simple: I do
Present progressive/continuous: I am doing
Present perfect simple: I have done
Present perfect progressive/continuous: I have been doing
Future simple: I will do
Future progressive/continuous: I will be doing
Future perfect simple: I will have done
Future perfect progressive/continuous: I will have been doing
As for the differences:
Simple: actions conceived as whole/unitary; sense of completion & permanence
Progressive/continuous: actions seen as 'in progress'; sense of duration & temporariness
Perfect: actions viewed as finished or continuing in a time up to a later time; retrospective
You don't have to know this all so don't be afraid if you get them confused at times, what really annoys me when it comes to grammar nazis is that the point of language is to get meaning across. "Do I understand what this person is saying? Have they got their meaning across and do I understand what they're communicating?". Accuracy and fluency are different things. Are you a student who is learning English so they can do a masters in a certain subject and then going back home? Then yeah you should probably learn all the finer details. Grown adult who is learning English as their third language just for communication purposes to improve job prospects or whatever? Then no and tell anyone who is acting all smarmy trying to correct your grammar to fuck off.
Hope this helps!