After installing the randomizer, you can start Ori and the Will of the Wisps Randomizer.exe which will open a Launcher from where you will be able to do everything you need in order to play the randomizer.
Firstly, you need to generate a seed. A seed contain the necessary information for your randomized playthrough, like the content of each item. You can generate them yourself by using the seed generator integrated into the launcher. You can find instructions on how to use the seed generator here. For beginners, we recommend to play with the Moki preset and the All Wisps goal.
After generating your seed, the game should be launching. When you reach the main menu, you can try to press Alt+L which should display a textbox with some information about the seed. If nothing appeared, the randomizer failed to inject itself into the game. It can happen if your game take too long to launch (in that case, the launcher should warn you about that issue), if your anti-virus is blocking the code injection process or if it deleted the Injector.exe file located in the randomizer installation folder (which you can open directly by clicking on the right icon on the Home tab). If Injector.exe is missing you need to reinstall the randomizer.
Instead of generating a seed yourself, you might have downloaded a .wotwr file from someone else, in which case you want to double click on it. It should ask you which program you want to use in order to open this type of file. Choose to browse for more apps on your computer and search the Ori and the Will of the Wisps Randomizer.exe which is located where you installed the randomizer. Once you have associated .wotwr files with the randomizer launcher, you should not have to do this again and simply double clicking on a .wotwr file will launch the randomizer.
Once the randomizer launches successfully, you simply need to start playing! It is recommended to play on a new save file because the randomizer will also affect save files made with the base game. If you ever feel lost when playing a seed, you can open your map and use the In Logic filter which will show you every item you can collect with the skills you have. You can also read the paths section of the seed generation to learn more about what the randomizer might want you to do. The community is also able to help so don’t hesitate to join the Ori speedrunning Discord or the randomizer development Discord if you need help with something!