I'm writing a script that posts automated messages as me. I having a hard time finding my user token. Do I have to create an app?
Yes, you have to create an app in order to generate a user token. You can create an app from here: https://api.slack.com/apps. Then you add the necessary scopes like chat:write, groups:history (in case of a private channel), and groups:read (in case of a private channel) from the OAuth & Permissions page and install the app. After you install the app, you will find your user token starting with xoxp- on the OAuth & Permissions page.