In this page we closely follow the YouTube tutorial but give a more textual explanation about everything.
Episode 1: Setting up IDEA, Basic mod class and first block
Download the MDK from: https://files.minecraftforge.net/maven/net/minecraftforge/forge/index_1.14.2.html Extract it somewhere and open 'build.gradle' as a project in IDEA (or Eclipse). IDEA will now import the project. After a moment it is ready and then you can open the gradle task bar and run 'genIntellijRuns':