The game Counter Strike: Global Offensive does not normally have admin commands built into the game.
To add admin commands, we recommend that you Install Sourcemod/Metamod, which is a framework for extending any game built on the "Source" engine, created by Valve.
Sourcemod's normally used to add support for plugins/mods, but it also adds an entire set of admin commands that make it much easier to manage players and the server. Many of these commands are practically essential if you're managing a public server open to all, and sanity-saving quality of life improvements.
Sourcemod is managed and developed by the group Allied Modders. Their website has a lot of useful information about Sourcemod and Metamod, at https://wiki.alliedmods.net/Main_Page.
Alternatively, you can also an RCON tool to connect to the server, but this only offers a limited set of commands (commands built into the game, but can't be used from within the game). Sourcemod/Metamod will offer many more commands.
We have a separate article on the actual process for installing Sourcemod/Metamod, which you can find here. The article does mention several other games besides CS:GO, since, as mentioned above, it can be installed on most games based on the "Source" engine.
The Allied Modders wiki has instructions on how to add and setup admins within Sourcemod.
List of Admin Commands
A list of Admin commands can be found on the Allied Modders website as well.