Imperialism has three different types of active unit:
Some of each type are available at the start of every game; others must wait for specific technology to be researched/purchased. All appear for use in the turn immediately after the one in which they were ordered.
Naval units are either merchant ships (which do their work unseen) or warships (which the player can move from one sea zone to another or direct to do one of a few specific things in one sea zone). Both types are built in the Shipyard at no monetary cost but with varying amounts of resources and/or materials (and for warships arms) depending on the precise model of ship. Early models use a lot of fabric, for sails, but later models tend to replace the fabric with coal and steel.
A unit of one of the other types uses up at least one citizen and has a monetary cost and at least one other requirement. Both can move fairly freely, and almost instantaneously, around your empire and in limited circumstances into and between other nations' provinces.