After installing TWRP and installing some ROMs via adb sideload, (or this story with my old Nexus 7) i learned that there is another way for installing Custom ROMs:
- Boot in to recovery (Samsung: Home Button + Power + Volume Up)
- Copy the ROM.zip to the SD card of the smartphone
- and then follow this screenshots
Click on "Install"
Click "Select Storage"
Select your SD card
Select the ROM you want to install:
Swipe to the right
Then some of the ROMs (like Prometheus) will guide you through an installation wizard, where you can chose some options.
If you want to try Prometheus you can download it here.