Thank you, is there like a video on how to do that?

Login to developer mode, Go to settings --> Technical --> Automated Actions --> Create new
Action name: Give your name
Model: Choose Purchase Order
Activity to so: create Next Activity
Active: on
Trigger: On Update
Trigger field: Status
Domain: Status is not purchase order
Apply on: status = purchase order

Activity: Task Complete (or choose any)
Due date in: 0
Activity Users : specific user
Responsible: YOur name

Alternatively, you can create an automated action to add followers on the creation of a purchase order so they get notifications automatically.

Thanks but I get a slightly different menu. I have Actions, Window Actions, Server Actions, Configuration Wizards, Reports & User-Defined Defaults. I tried creating an action but I dont get the options you present here. Server Actions does have similar options but I got stumped at the Activity To Do becaue Create Next Activity is not an option there, only Execute Python Code, Create New Record, Update Record, Execute Several Actions, Send Email & Add Followers. Would it be Several Actions?

Keep scrolling down the technical dropdown till you see automation ( Automated actions, scheduled actions etc...)

If you still don't see it, try installing the module

install module: base_automation

Duh...sorry, found it. Ok but I still dont get the option Create Next Activity. I do get the Trigger Condition and for domains i get a code editor. I dont get Activity Task or Activity Users. So i cant finish the action...any other suggestion?