Question: How do I keep players from accessing certain commands?
I'm making a server and these kind of things are thing i need to know

Answer: 
Adding on to @Unionhawk's answer you could aternatively just use a permissions plugin such as [Group Manager](http://wiki.ess3.net/wiki/Downloads) or [PermissionsEX](http://dev.bukkit.org/bukkit-plugins/permissionsex/) with Bukkit along with the [Essentials plugins](http://dev.bukkit.org/bukkit-plugins/essentials/). I'd definitely recommend reading some guides on running a Minecraft server, [this not the best guide](http://www.wikihow.com/Run-a-Successful-Minecraft-Server) but a guide nonetheless and should point you in the right direction. Just google around to try find a guide that will suit you best in your objective.
there are 3 steps-
1. In order for players to be able to break blocks near spawn, (spawn protection) they must be OP. So OP them.  

2. close the server, and open the server.properties file .
3. change the OP permission level to 1. this will restrict all OPs, so they no longer have commands. But, they can still break blocks around spawn.  

 If you want to run commands, you must run them out of the server console.