There are a few ways.
Adding scripts from the SDN
While logged into your forum account, go to the link below, and click "Add" on any scripts you would like to appear in your bot
https://osbot.org/mvc/sdn2/scripts/
Adding manually
To add a script manually, you'll have to find it in one of these sections. You will need to download the .jar file for the script and put it in your OSBot folder.
The folder is located here:
C:\Users\*YOUR ACCOUNT NAME*\OSBot\Scripts
https://osbot.org/forum/forum/288-downloadablelocal-scripts/
If they aren't appearing as burnmeh said, you can hit the refresh button and they should appear. If not, close the bot and run it again. Or redownload the newest version of the bot
http://osbot.org/mvc/get