First thing is to open up any browser on your PC and go to the link below.
From the menu, navigate to the server that you want to add StenBot to and click it.
Make sure you have the Manage Server permission on the server you want to invite the bot to otherwise it will not show up in the list.
Then check the verification box and you should see your bot in the server.
Double check that the bot has administrator permissions. If that's all good, then you're ready to move onto the next part.