That is because these things are
arguments, not
commands. They are things that add onto a command. What you've been doing, to give you a comparison, is to try to hang your christmas tree ornaments without having a christmas tree. Of course they won't stay put in empty air and everything will "crash"
The actual command you need to give your computer is "launch a program". Then you can add the arguments that say "...and launch it specifically like this".
Minecraft is a java program, so your command is "java" or "java.exe" (both are equal). It tells your computer to "launch a java program". Which one? That is specified with the first argument: "-jar minecraftforge-universal-1.6.4-9.11.1.953.jar". Depending on what version of forge you are running, that name might look different for you. So, now you are telling your computer: "launch a java program, specifically this one". And then you can copy the rest of the arguments you found in this thread
after what you already have. Then you final command says: "launch a java program, specifically this one, and do it with this much memory and this garbage collector configured like so" and so on.
java.exe -jar minecraftforge-universal-1.6.4-9.11.1.953.jar -Xms2048m -Xmx2048m ...and so on and so forth