In your title you have that you're running a CSS Server. If that's the case then you're not running a HLDS game, but a SRCDS game.
Assuming you are running a CSS Server then AMXX is a mod for the HLDS engine in which case won't work here. So you'll want to look into Sourcemod. Sourcemod has a some built in features for map vote management. By default it will start a vote near the end of the map and the players can vote for what map they want. You can also find a plugin called rockthevote.smx that will be located in the the ./sourcemod/plugins/disabled/ folder. Move that plugin from the "disabled" folder into the plugins folder. This will enable your players to type rtv, or rockthevote and so forth to force a map change if they don't like it. The first time the plugins is loaded you'll find a new config file that was automatically created in your ./cfg/sourcemod folder. You can tweak the settings in there to fine tune the plugin.
You can get sourcemod from
here but keep in mind you will also need to have Metamod: Source installed. This can be found
here. Be sure that you create the metamod.vdf file and make sure you use the correct OS and gametype when creating the .vdf file.
Now if you just had a typo and are running a CS 1.6 server or any other mod on the HLDS engine, you'll want to look into AMXX mod. You can find AMXX
here. I recommend downloading the full auto installer and following the prompts there. AMXX still has it's own basic map management tools, however most of the configs will be found in the ./addons/amxmodx/configs folder. Now AMXX doesn't have a built in rockthevote feature like Sourcemod, however there is one available, as well as other map vote plugins that have alot more features then the default one.
Hopefully that answered all your questions