Configuring Linksys WRT54GTL as Access Point to Extend Wifi

Hello,

I have xfinity internet service with an XB6-T gateway.  I would like to extend my wifi network to help with coverage in a part of my house where the service is weaker. I have an older Linksys WRT-54GL wireless router and I understand its possible to connect this to my XB6-T gateway via ethernet cable to create an access point and therefore extend my wifi network to that part of the house. I'd like to understand the steps to do this. Thanks!