First, register your company with the FDA. Search for "register establishment" on the FDA medical-devices website. Upon registering, you become potentially subject to FDA inspection.
Second, review your products to determine their FDA classifications (Product Code, and Class), which may not be the same as those under MDD. A number of MDD Class I and I-s devices are FDA Class II, and some FDA Class I devices are MDD Class IIa. Also note that a few FDA Class II devices are 510(k) exempt, and some FDA Class I devices do require a 510(k).
Third, for any device that will require a 510(k) prior to initiation of marketing, prepare and file that 510(k), or work with a consultant to accomplish that. The normal timeline after filing is the full allowed 90 days; more time will be required if they request changes or more information, which is fairly common.
Fourth, list your 510(k)-cleared products on the FDA registration-and-listing website.