I am new to it since i downloaded forge and eclipse.
Did you learn Java?
"We live on a placid island of ignorance in the midst of black seas of infinity, and it was not meant that we should voyage far."
As long as you understand Java and JSON you'll be good. Watch a few tutorial (I recommend SilentChaos512 and McJty) or find some documentation to get you started. Ask the Forge forums even if they have any pointers.
https://www.youtube.com/results?search_query=forge 1.12.2 mod tutorials
https://www.youtube.com/results?search_query=silentchaos512 mod tutorials
Modder Support (Java language experience is expected before posting)
Forum Thread Maintainer: Asphodel Meadows, Fabric Project, Legacy Fabric, Power API, Rift/Fabric/Forge 1.13 to 1.17,
Niche Community Content Finder, Youtuber, Modpack/Map Maker, Duck
Major Forums I Maintain:
Fabric/Forge 1.16: https://www.minecraftforum.net/forums/mapping-and-modding-java-edition/minecraft-mods/mods-discussion/3004971-fabric-1-16-snapshot-discussion-thread-for-20w06a
Asphodel Meadows: https://www.minecraftforum.net/forums/mapping-and-modding-java-edition/minecraft-mods/mods-discussion/3058934-asphodel-meadows-datapack-info-thread-wip