I went to the installation page and tried to find the build.gradle but could not find it what so ever thus i am unable to start my game as it is required for a mod I'm using. I'm trying to install the 1.15.2 version.

Drag and drop the mod into your mods folder. The wiki is for developers only. https://www.curseforge.com/minecraft/mc-mods/geckolib/files/3034409