Discovery is the process via which opposing sides in a lawsuit exchange information. In general, the scope of discovery is pertinent to claims or defenses.
There are several types of discovery tools. These include requests for admissions, interrogatories (questions), depositions (interviews under oath & penalty of perjury), requests for production of documents and tangible things, and requests for physical & mental examination (if at issue in the lawsuit and upon permission of the court).
In general, discovery is a judicial process that the court is not actively a part of. If the parties disagree on the process, they must first meet and confer to attempt to work out the matter. Only then can one party or both make a motion.