Movement and Position

In combat, characters and monsters are in constant motion, often using movement and position to gain the upper hand.
On your turn, you can move a distance up to your speed. You can use as much or as little of your speed as you like on your turn, following the rules here.
Your movement can include jumping, climbing, and swimming. These different modes of movement can be combined with walking, or they can constitute your entire move. However you're moving, you deduct the distance of each part of your move from your speed until it is used up or until you are done moving.
Breaking Up Your Move

Difficult Terrain

Being Prone

Interacting with Objects Around You

Moving Around Other Creatures

Flying Movement

Creature Size