A Hover Vessel is a type of hover craft. It is only useable on the surface of a planet. To build one you need a Hover Vessel Starter, which is made by combining a Core (Player), and 8 Hull Blocks in the Large Constructor. It was formerly known as Ground Vessel. The name was changed in release Pre-Alpha 3.0.0 because 'GV' and 'CV' looks similar.
Block overview: Hover Vessel
A Small Vessel is a flying vessel that can fly around within the atmosphere of a planet as well as enter space and reach moons and asteroids. To build one you need a Small Vessel Starter, which is made by combining a Core (Player) and 8 Hull Blocks in the Large Constructor.
Block overview: Small Vessel
In order for a Capital Vessel to be fully operational it requires a Generator, a Fuel Tank (Small or Large), a RCS, a Cockpit, some Thrusters, and a Gravity Generator. It can also be outfitted with a Warp Drive and a Warp Drive Tank to reach other planets.
CVs are able to be constructed planetside or in space, however certain CV weapons only function in space.
Block overview: Capital Vessel
A Base is not a vehicle, but instead a structure. The base is similar to your Capital Vessel, except that it cannot move and is for planetside operations. To build one you need a Base Starter, which is made by combining a Core (Player) and 8 Hull Blocks in either a Mobile Constructor, or Large Constructor.
In order for a Base to be fully operational it requires a Generator, and a Fuel Tank (Small or Large). The fuel tanks also require Fuel Packs. (Refer to Fuel Tanks). Once powered, a base can contain a multitude of different tools, provide you with safety, and support you while on the planet's surface.
Block overview: Base