Hi.

1) Download this (proceed via instructions on that webpage) - What you NEED is Mod Installer and Patcher

2) Place them inside your game's directory (where you see stuff like "bin", "cpk",...)

For regular mods (= ".x2m" files):

1) Start Eternity's Mod Installer. Using it's easy-to-understand buttons navigate to your desired mod. The Installer will install it and now you have it in your game

For mods that are in different format than ".x2m" their creator usually leaves an installation guide somewhere from where you downloaded them or inside a folder that you downloaded.

Note: If you are using a mod and run into an infinite loading screen when attempting to start a VS battle, PQs,...; that means there was either a mistake made by you during installation, or the mod itself is faulty or relies on data and resources from other mods. If it is the latter, modders usually mention what other mods you need to have installed in order for their mod to work. If no such mention was made and you are certain you did nothing wrong, the only choice left is to contact the modder directly via a method of your choice.