Configuring your mods through files.

1 - Find a mod that supports Cloth Config API.

2 - Open the "%appdata%" folder and the ".minecraft" folder inside it.

3 - Download the mod and place it into your "mods" folder with Cloth Config API.

4- Run the Minecraft and close it after.

5- Open the "config" folder in ".minecraft".

6 - Find the file that contains your mods name/id.

7 - Open it with a text editor.

It should look like this or similar to this.

Now you can configure the mod by using the options in the text editor. Remember to read the option's name and its comment if there is one.