Communicate with teacher from breakout rooms

Hello. Thank you for two questions.  

For Q1 - How do I let them put their hands up or similar to show that they're done with an assignment? I would suggest when you set up the breakout rooms, you allow them to return to the main room since they are done with their assignment. There is no feature where they can raise their hand from the breakout room to let you, the Host, know they are done. 

For Q2 - How do I let students chat with me in the main room from inside the breakout room? The students in a breakout room can chat with other users in their breakout room, but they can't send you a chat message. As you mentioned, this is what ask for help is for in Zoom. You will get an alert and be able to join their breakout room.

Now, you could allow them to leave the breakout room, return to the main room, and send you an individual chat if you enable that feature.  One last item for this question, thinking outside the box, you could create a breakout room for yourself and have a student pop into that room and ask a question.  They could also just ask you a verbal question in the Main Room. 

I hope this helps. Please let me know if you have any other questions. Thank you!