It is treated by removal of the affected testicle. It is called an orchiectomy. You may or may not need chemo therapy too.

You will still be able to have children.

Some time after surgery you can be fitted with a prosthetic testicle. It is a silicone ball matched to your other testicle and implanted in your scrotum.

edit: Well surgery is surgery. There will be some discomfort. They do have pain medication though.