Help understanding build.gradle and how to add mods to the project.

2023.2

So I'm making a RPG mod that centers around forcing the players into a specific role or class that uses variables to determine they are or are not that class, and allowing/disallowing things to be used properly if you are a specific role. standard stuff, and things are going smoothly! Mage spells look really fancy~

However. I'm writing this because i've hit a REAL road block.

how on earth do i add a mod to the project so i can test damage numbers? like a damage indicators mod? (because some of the damage may be modified by other sources) and on that note, is it possible to add other mods to the project to make sure they fall inline with the role rulesets? warrior/mage/thief etc.

when i drop the jar file in the mods folder it crashes the launcher, regardless of what it is.

the only HINT of what i'm supposed to do is "Import it with the build.gradle". a what?! I have no idea what that is, and when i found and opened it in a text viewer i'm equally 200% lost.

It is implied that build.gradle can be opened with an app, and "Used" to import a mod to the project that i can SEE and USE within the project.. I downloaded a THING from the Gradle website, followed the installation process, and i'm STILL lost on what i'm supposed to do with it.

but the only HINT i got after many google searches does not elaborate on HOW to import with build.gradle so that my MCreator project knows what to do, i'm completely stumped.