What does it mean to command creature up to lvl 3? I know what command creature means, but up to lvl 3, what does that mean?

Creatures and NPCs have character levels, similar to your player character.

Command Creature to Level 3 means that if the creature is at level 3 or below and you have 100% spell effectiveness, then the spell will work. Otherwise nothing will happen.

There is no in-game way to tell the level of a creature (or NPC) without being on the PC and using the console. Also if you are wearing armor then the spell effectiveness is reduced. So a Command Level 3 spell might only work on level 2 creatures.

Command Creature up to Level 3 is a very weak spell.

However if you get a Command Creature Level 25 and 100% spell effectiveness, then the spell will work on all creatures, even if above level 25.

Most enemies are well above level 3, so that spell will only command the early creatures.
Do not try to use it on anything other than deer, mudcrab, rat or wolf.

Later on you can buy a stronger command spell or custom make your own.

As Savlian has said, Command Creature level 25 is the max.

Ok, thanks guys.