Just signed up and have questions

I (67F) live in a rural area and they've just put in fiber optic which is very exciting as I've had wireless for years and would love to have 4K TV etc. I've signed up for installation next week and didn't do the monthly modem plan. I am fairly tech-savvy but not with networking etc. I'm wondering if the router I have is enough. I also have a Google Nest modem/router which I think we got to extend to the other side of the house. My hubby set it all up and he died last year and I'm trying to remember the why's and wherefores.

My question is...do they come in and just use the router I have and set it up? Even if it's not their equipment? If I keep the same router will anything change other that it has something different plugged in? WiFi name and password for example?

I have an ASUS RT-AX58U which is "AX3000 Dual Band WiFi 6....lots of features...."

Is the Google Nest my modem? Or do I need a separate modem? Please help without talking about high splits and other things that will confuse me. Believe it or not, I'm the one my friends call for tech help but this stuff confuses the poo outta me. THANKS