Firstly, this is found more fun for map types like fun yard and/or a gameplay which respawns you
after death (eg. CSDM). Secondly, In simple terms, "Upgrades" are special abilities. Players can choose from varieties of upgrades to fit their playing style. Each upgrade uses "slots" which are obtained by leveling up. So the more you have, the more upgrades you are able to use.
(Open Readme for more information and installation help)