If you haven't used a jetless upholstery tool before it can take a bit of getting used to.
The main difference is that if you press the trigger with the tool off the fabric the solution will be sucked straight up the vac slots and that is the key to getting the flow setup properly. Ideally when holding it in front you and press the trigger you should see solution coming out of the slots and then being sucked into the tool. There shouldn't be solution firing out beyond the vac slots, so just trim it up and away you go.
Simon