Welcome and I'm glad you asked about the threads. Roni has done a great job describing them but I'm here to encourage you to participate.
I'm amazed at how freeing it is to just know you have to only paint for 20 minutes and see what you have come up with - without judgement since you know it only took 20 minutes. I also find that if I want to work a bit longer, it's really not a problem.
For me, and I think the others will agree, what works best is doing these from real life - start perhaps with what you can find in your fruit bowl or refrigerator. If you go back you'll see lots of eggs, apples, oranges, etc... Working from life is good practice and for me I like how I can see more colors than in photos.
All levels are welcome and it's just fun to join in and see what we all capture in our lives. I do recommend you go back and see what the previous weeks have been like - this one seems to have taken a bit of a tangent into more detailed work. Not typical. It may be that more folks have time since the holiday.
If you can't think of something to paint, just ask and we'd be happy to make recommendations.
Can't wait to see your work - you'll love this community!!!