Thanks guys that pretty much covers it, but my questions becomes then could say a wizard use any lvl 1 spells in that spot say day one I take burning hands magic missile and something else, but day two I want magic missile, but don't want the others can I just pick different spells?
If you are playing a wizard, be aware that you can only prepare those spells which are in your spellbook. Generally, wizards do not have ALL of the spells of any given level in their spellbook (except for level 0 cantrips). Effectively, you have two spell lists. The first is your spellbook, which is a record of all spells you are currently capable of memorizing. The second is your list of prepared spells, which can only be filled with spells that are in your spellbook. As you gain levels (or gold), you can add to the spellbook whenever you are able. Your prepared spells are strictly limited by your level and your bonus spells for your high Int.