When you open PornMD/gay, you will see a search box, along with the option to choose between straight, gay, or trans porn. You will also be able to search for content only from a specific adult site. They include content from PornHub, ModelHub, RedTube, YouPorn, and Tube8. You can also just select PornMD, and then your search results will include the content from all these sites.
You can also choose between videos and photos, plus it’s possible to search by voice. The search engine will suggest keyword tags as you type. No matter what you type in, you’ll probably get tens of thousands of results, and you’ll then be able to set various filters and apply a few sorting options.