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: 
By default, the majority of commands (with the exception of `/me`, `/tell`, `/help`, and `/trigger` for some reason) are restricted to server ops. Players are, by default, not allowed to use any other commands on a server. Server ops can use other commands. You can specify ops in the `ops.txt` file, or by using the command `/op <playername>` in the console, or in-game (assuming you have added yourself as an op).

By default, server ops have access to all commands, including commands like `/stop`. You can change this by modifying the `op-permission-level` in your `server.properties` file. Setting it to 4 (which is the default) allows ops to use all commands. Setting it to 3 restricts the `/stop` command, setting it to 2 restricts server moderation commands (`/kick`, `/ban`, `/op`, `/deop`), and setting it to 1 removes all special permissions from ops other than the ability to bypass spawn protection. You can still use all of these commands in the server console.
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.