There are no built-in admin commands in Counter-Strike: Global Offensive by default. To be able to execute admin commands, you have to install Sourcemod/Metamod first, which is the base for extending any game built on the Source engine. Then you need to make yourself a game admin of your server.
To install SourceMod or MetaMod, use our instructions «How to Add SourceMod or MetaMod to CS:GO Server».
To become a server admin, use our instructions «How to Become a Game Admin on CS:GO Server»
You can find a list of all the admin commands on the following website – https://wiki.alliedmods.net/Admin_Commands_(SourceMod)