A character’s Speed is how fast they can move, which, unless otherwise noted, is 6. Often play is done on a grid with 1 inch squares or hexagons representing roughly 5 ft. or 1 meter each. So a hero with a speed of 6 can travel up to 6 spaces horizontally or diagonally.
You can move through spaces occupied by allies (or enemies as difficult terrain: half speed), as long as you don’t end movement in an occupied space.
For a quicker, more loose game, you can forego counting spaces and measure typical movement roughly from pinkie to thumb. Slightly less for players with large hands (or slower characters), a bit more for our tiny-handed friends (or faster characters).
When a character is forcibly moved but stopped by an obstacle, they take 1d6 bludgeoning damage for every space this movement is shortened. If they hit another creature, both creatures split this damage. Falling inflicts 1d6 bludgeoning damage for every 10 ft. fallen (2 spaces).