In Minecraft, doors are great for keeping things out, or keeping things in if you’re into that kind of thing.
Doors only come in two flavors.. wood, and iron.
Wooden Doors can be clicked open, but Iron Doors need a button, switch, or pressure plate on an adjacent block to be opened. Or you can get super fancy and make use Redstone Dust to make redstone circuits to open your doors.
Arrange your blocks as shown in the pictures below. You only get one door per combination.