Although David used a child FLO to demonstrate his example above, it doesn’t need to be in a child FLO. You could just add the Object Get and the Continue If cards to your FLO wherever necessary.
If you do decide to stick with the child FLO you’ll also need to add a “Return” card after the Continue If card in the screenshot and drag over the “Output string” from the Object Get card. To run the child FLO, you would just use to Control - Call FLO function wherever necessary.
Dynamically pulling info from Slack and adding it to the Get card is definitely possible. I’ve included an example screenshot of what I believe you’re trying to do below.
You just drag the fields into the compose card wherever you’d like them to go and type the structure around them to match the way it’s set up in the Object Get.
Does this work for your scenario? I’m not sure how dynamic you’re trying to make this list so I wasn’t sure if this fits your needs.