Movement outside of combat is rather cut and dry, allowing for more freeform roleplaying and less roadblocks to get to the bulk of the storytelling. Within combat, however, there are several different ways to cover how fast characters, enemies, and their summons move. Depending on whether or not you want to use a grid.
When using the gridEdit
When using a combat grid, characters may move a number of squares equal to their Dexterity score per turn. This means that quicker, smaller creatures close in faster, while a heavier creature may take its time lumbering towards you, giving you time to prepare spells.
Without a grid, using feetEdit
When measureing in feet, characters move at a rate of their Dexterity score yards per turn. With the same idea as above. Making sure characters move equal to their rating in hand eye coordination.
Make sure that characters are moving in a way consistent with their Dexterity score. Slow things should be moving slow, fast things moving fast. In general a creature with 2 Dexterity should move twice as slow as a creature with 4 Dexterity. As long as you're living up to the spirit of this, don't sweat the details too much.