How do we create an server and know the IP of it??
you mean dedicated server? or just lan server for you and your friends?
in first case there is a folder located in game archive called dedicated/ with dedicated binary files. and sample server config near. IP will be the external IP of your server\PC where you starting dedicated server.
in second case you just can use multiplayer menu and subitem "create" where select game type, map, mutators like akimbo or minsta or rm, start weapons and all other things. for lan party check your IP in your network card|wi-fi adapter settings, depending youe connection type
to get your external IP open "https://ifconfig.co/" site for example