Mine Craft Comes Alive... Help

Hi,

So I've been trying to add the Minecraft comes alive mod to my server. It told me to download it onto my computer so I did and I also downloaded everything else that is important for the mod to work. Even after doing that It says

"This server has mods that require FML/Forge to be installed on the client. Contact your server admin for more details."

I don't know what I'm doing wrong but this is my first time trying to create a server with a mod on it so I'm a noob at this.

Please help.

Ps. Aternos is extremely helpful. Thank you

How/where do I forge the profile in the minecraft launcher?

EDIT: Nvm I watched a youtube video about what forge is thank you Roman and Jervy!