It may not seem very obvious, however if you are able to provide some insight into the lump, one can get closer to the true diagnosis. Are you able to explain the following about the lump-
The location. Front or back of hand. Which finger. Base, middle or tips of finger?
The pain. If present, continuous/intermittent nature. What brings/relieves the pain.
Swelling. Overlying skin colour. Feel of the swelling. Is it mobile? Does it change in size. And how does it bother you? Does it stop you from doing anything. How did you first notice the swelling.
Is your ability to do daily tasks affected. Is your grip strength ok? Is the sensation in the hand preserved?
The big list of questions may seem overwhelming but it is important to ascertain them before any further steps.