Home office networking

Hello

I have a desktop computer in my home office along with a router and modem. The computer I have in the office and my laptop shares an internet connection. I have two questions

1. How do i share a connection with one printer.

2. I recently brought a computer from my work office to set up for my children to use. This computer is upstairs. I was wondering if i can set this computer up to share the internet and printer connection i already have set up. Please help. I have spent hours of reading on the internet figure this out. I am not very computer savvy. Would appreciate some guidance. Thank You