It sounds like you're trying to treat AE like just another piece of software, and it's no big deal to learn it.
Well, it is a big deal. You need to start with the basics, and you build on them.
Trim path is the wrong tool. You need to overlay mask path on your text and then add Stroke to the mask path, then have it either reveal the original layer or use the animated line as a track matte for your text. There are a ton of animating handwriting tutorials on the web. You'll find something that will get you started on Google.