Discord Bot Studio requires your bot token to be entered on the Setup page. This page explains how to find that token. To do so visit the following link: https://discord.com/developers/applications.
Once there, click on the bot you are working with. Next, select the "Bot" tab from the left hand side:
Finally, click the "Copy" button next to the bot's avatar to copy the token to your clipboard. Then you can paste this into Discord Bot Studio in the token field on the Setup page.
Keep your token safe, and never share it with anyone else!