Mods not working

Put the summary of the bug you're having here

What I expected to happen was...:
I got a mod for java edition and wanted play it.

What actually happened was...:
When I tried launching java with the mod it says the game crashed and that there was an error

Steps to Reproduce:
1. I got to mincecraft launcher.
2. I select java and select the mod I installed using forge.
3. I launch it and it says the game crashed and that there was an error.