Randomizers have logic that restricts the way the items can be randomized. For example, in the default mode of the Link to the Past randomizer, you need the boots to get the item off the top of the bookshelf in the library, so that item will never be the boots. You need either the lamp or the fire rod to get through certain caves and sections of palaces, so you're guaranteed to be able to find either the fire rod or the lamp prior to having to complete those palaces.

Using glitches can help you "sequence break", to a certain extent - if you use a glitch called "fake flippers", you can reach certain areas of LttP that would normally require the flippers without having them. You'll never be required to do so to beat a seed in default mode, but doing so can save a ton of time if there's a required item blocked by the flippers and the flippers are a pain to get.

The LttP randomizer also includes "glitches required" modes, where varying levels of glitch execution might be required to complete the game, and the logic is relaxed accordingly.