The unified spell progression works by assigning each class a base magic bonus and then comparing that base magic bonus to a single spell progression chart. A Wiz6, a Clr6, and a Wiz3/Clr3 all have a base magic bonus of +6. Each of these characters has exactly the same base spell slot allocation (the unified progression is based on the Wizard progression so I suppose it would be 3/2/2 for 1st, 2nd, and 3rd level spells-- off the top of my head). The base magic bonus concept can be seen in Unearthed Arcana.
The table indicates the number of spell slots and ready spells that the character receives. Each rest period, the spellcaster prepares his ready spells: that is, those spells from his class spell list that the caster wants to have access to. There is no need to ready multiple "copies" of the same spell-- for example, if you ready magic missile, you can cast it as many times as you want, provided you have the spell slots to do so. The ready spell mechanic can be seen in Monte Cook's Arcana Unearthed.