I actually had 5 lymphnodes removed from my armpit when I was 14. Three were solid, two were fluid filled. None had cancer.
If you are having a needle biopsy, they will numb the skin with lidocaine or an equivalent. It will poke and sting a bit. You might have some minor discomfort when they take the biopsy, and you might not notice a thing.
If you are having surgery, which is what I did, I had them removed; then you should talk to your doctor to get more information. For me, I spent two days in hospital. I seem to remember taking a couple of months to feel normal, but I was using my arm within a few days. I had minor swelling in my arm for awhile. The doctor nicked a nerve (there are a lot of nerve branches in the axillary--armpit-- region. So the back of my upper arm felt like it had a mild burn/ numbness when people would touch it. The doc said it would heal slowly over time, and it did.
The best thing you can do is breath. Try to relax. You will know the results soon enough and can make an action plan if needed. I wish you all the best.