@CheleB Definitely not dumb, this gave me a moment of pause too when I installed it on my linux laptop. I'll give you two different ways to do it, just in case.
The easy way: Find "TechnicLauncher.jar" in your file explorer, wherever you saved it. Right-click it and choose "Open with." Select the option that looks something like "Oracle Java 8 Runtime." That should do the trick!
The terminal way: Open a terminal, and move to the location of "TechnicLauncher.jar". If it went to your Downloads folders, something like:
...should do the trick. Then, type:
java -jar TechnicLauncher.jar
...and press enter. That should works just as well.
Let me know if you have any more problems!