In this case you would want to change the audience field to 'Any contact in my audience' to allow anyone to trigger this. I'll include a screenshot of this below.
If you're wanting to just do a single send, you would just want to create a draft and use 'Review & Send' from within the mailing. For more info on building an automation workflow check out our documentation here:
Lastly if you're looking to branch off of a mailing but don't have a trigger in mind to start off, you can try reimporting and mapping a date contact field to utilize a date trigger. In this case be sure to set the date 2 days in advance. Feel free to read over our documentation on this here: