I'm sorry for what is probably a dumb question. How can you tell what fabric a tent is made of?

I have a 1995 (approx) REI nitelite that I am considering repairing the waterproofing seams. But there are products for "silnylon" and regular(?). The seams have tape on them so I know I'll need to get off what I can of that. I'm also not sure if I need to use this sealant (see link), just tape, or the sealant and tape: