Hey friend.
The traits are used to determine what kind of effects a color will get. For example, if you give it the "Gentle" trait, that color will get healing effects.
The Names, titles, and descriptions are used to generate card names. So let's say you make a mod that features an image of Goku, you can enter "Goku" in the Unique name slot. If you get a rare card that features that image as the card art, that name can be used in the name generation, so you could get "Goku's Rage" or whatever fits the effect that card has.
Names are completely optional. The game will just generate other names if the image doesn't have any particular names or titles.
Lastly, to use a mod, you just need to click the "MOD" button in the main menu, click the mod you want to use once (It will highlight in blue) and then just go back and start a run.
Edit: There is no proper documentation for the traits. I do have a list for them in the game's Discord server but nothing easily accessible. If you want them, let me know and I can send it your way or invite you to the discord server.