there are videos here https://www.trapcode.com/form_training.html that should give you an idea of how to set it up. Especially the “using layer maps” tutorial
also, there used to be a project available to show you how to make text disperse and fade out, but it’s not on the site anymore. It’s called texttosand.aep if you want to look around for it. Someone here posted a link to it in another thread about a month or so ago. I downloaded it at the time, and have it somewhere.
I messed around with that project file and figured out how to get the text to coalesce from particles into words. Basically I removed one of the ramps for opacity (i think) and reversed the direction of the dispersion layer (i think… maybe vice versa), then put that into a comp and time reversed the layer so that the particles would work in reverse. I tried a bunch of different techniques to control the particles, but this is what eventually worked.
hope that helps.