Hi Marcelo,
You can use the Start/End Conditional Statement actions to determine whether your checkbox is checked. These actions allow you to run a subset of actions between them, but only if certain criteria are met. In this case, you'll want it to check the value of your checkbox.
You can then use the Start/End Loop Through Table actions to look for appropriate customers. These actions allow you to loop through a table for records that match specified criteria, performing actions on them one by one. In this case, you'd be interested in Customers of a certain Category.
You'll then want to use the Insert Records Into Table action, which you can configure to insert fields based on Value From Row. Value From Row means the currently selected record in a loop, so it'll take the current record in your Loop Through Table action, grab the specified fields for that record and insert them into your table. If you place this between your Start and End Loop Through Table actions, it'll be performed for each record found by your loop.
Hope this helps.
- Justin