Use your IDE for this. For example, if you are using "IntelliJ IDEA" and you correctly setup your project (jdk, forge mdk, gradle, parchment, etc.), then you can just use Ctrl + B with Block type selected. It will navigate you to class declaration.
I have installed a minecraft 1.12.2 server and java 8, but the forge-blahblahblah.jar file isnt doing anything, the minecraft server file is opening the server but as expacted, it just launches a vanilla server