DnD 5e - Mounts and Vehicles
If you choose to acquire a mount, whether something as mundane as a horse or as fantastic as a pegasus, you'll want to know a few things about how they work outside of combat. Similarly, if you have a vehicle like a cart or a ship, you'll need to know a few things. If you don't plan on doing either, skip this section and come back later.
The full stats for mounts, vehicles, and related items are presented on several tables on page 157 of the Player's Handbook.
Barding is armor for your mount. It costs 4 times as much as normal and weighs twice as much as armor for a humanoid. Still, mounts are notably easy to kill because they don't get tougher as your enemies become more deadly, so investing in some armor is wise, especially if your mount is difficult to replace.
Your mount doesn't need to worry about armor proficiency. Jeremy Crawford, the Senior Game Designer on 5th edition Dungeons and Dragons, explained that The rule on monsters and armor is purposefully generous. So as long as your DM is comfortable with your pony wearing plate, you're good to go.
Saddles come in several types, but generally if you plan to do any fighting you want a military saddle. Military saddles give you Advantage on any check to remain mounted. Those aren't common, but they do happen. Generally you make saving throws instead.
You need an exotic saddle for aquatic and flying mounts, which won't provide the benefits of a military saddle, which isn't great because being knocked off of a flying mount typically hurts more than falling off a horse.
If you have proficiency with a certain kind of vehic1e (land or water), you can add your proticiency bonus to any check you make to control that kind of vehicle in difficult circumstances.
Keelboats and rowboats are used on lakes and rivers. If going downstream, add the speed of the current (typically 3 miles per hour) to the speed of the vehicle. These vehicles can't be rowed against any significant current, but they can be pulled upstream by draft animals on the shores.
A rowboat weighs 100 pounds, in case adventurers carry it over land.