Boats are rideable objects placed on Water used to move faster through big watermasses.
Boat Riding
A player holding the Mineboat.
A boat floating.
Quite differently from the Minecart, boats moves accordingly to the player's will. The boat also moves significantly faster than a player on water but is slower than a Minecart. While some movement bugs are still present, it's possible to steer using the WASD keys. Boats also have movement relative to the camera, so it's possible to manoeuvre them with the mouse. Boat changes direction if in contact with, a player, another boat or a mob. If you ride a boat and crush into another boat your boat will get destroyed and the other one will just bump away.
Boats cannot be placed on terrain and will be immediately destroyed upon contact with solid blocks, resulting in a random amount of Wood and Sticks of leftovers. The same resources are gained when a boat is destroyed by the player. Boats also can not be used on Lava.
Like Minecarts add roller coasters boats can be used to make water slides. Boats are very fragile so it will be difficult to make advanced buildings.
Video of a player riding a boat. Video of a water slide, it also demonstrates boat to boat collisions.