I had an MRI on my shoulder-found bone spurs and swollen lymph nodes in my armpits. What does the swollen lymph nodes indicate? Should I be worried?

It depends. It depends on the size and number of enlarged lymph glands in the armpit. If there are only a few enlarged lymph nodes and they are only minimally enlarged (between 1.0 and 2.0 centimeters in size) then there is likely no problem. If there are many nodes and greater than 2.0 centimeters then you should be seen by your internist for further studies (blood tests and additional imaging studies).
Varies. You would certainly want to be evaluated for this. Lymph nodes are the " filters" for the blood stream and will be swollen if there is any infection or in some malignancies. I would just make sure you follow up with a physician after your MRI.