Hi,
Do you know Tom got an award?
No, thank you for telling me, that's great! The focus is on 'now'.
Did you know Tom got an award?
No, I didn't know, until his wife told me yesterday. The question is about the past.
That's the basic difference. A more 'advanced' difference is that in some situations we can use past tense in a question to 'distance' ourselves from the present, in order to increase the level of politeness. For example, a waiter talking to a customer:
Did you want to order now? is a little less forceful than Do you want to order now?
Best wishes, Clive