Choose a Launcher

It is recommended to use Shiginima as laucher, because it's easy to configure.

Java Settings

At the "Executable:" box, usually on the path textbox it is defaulted at - [C:\Program Files\Java\jre1.8.0_251\javaw.exe ] This is what the current java version that is available. Otherwise, you may have an updated version.

At the "JVM Arguments" box the arguments are written as 
-Xms4G -Xmx4G -Xmn128m -XX:+UseG1GC -XX:+AlwaysPreTouch -XX:+UnlockExperimentalVMOptions -XX:MaxGCPauseMillis=100 -XX:+DisableExplicitGC -XX:TargetSurvivorRatio=90 -XX:G1NewSizePercent=50 -XX:G1MaxNewSizePercent=80 -XX:InitiatingHeapOccupancyPercent=10 -XX:G1MixedGCLiveThresholdPercent=50 -XX:+AggressiveOpts   
   where: "-Xmx4G" is the amount of memeory your PC may be available. This is defaulted at "-Xmx1G", If ignored it may cause the client to hang. 

At the "Game Directory:" box, is where your ".mincraft" folder is located. In the example, the location is at D: drive if the PC.

At the "Use version:" dropdown, in order for release "1.12.2-forge-14.23.5.2854" to appear, prior to installtion, just execute the jar file "forge-1.12.2-14.23.5.2854-installer.jar". This will download all the necessary library files.

(Optional for debugging purposes)At the "Launcher Visibility" in this example, "Keep the launcher open" is set.

Once everything is set, you can "Save Files" to exit.