I just installed the Linksys

Question

I just installed the Linksys WRT54G wireless router however at no time did the installation ask for me to install security controls. How do I now convert the installation to a secure network with my own unique password? When I was installing the "make my computer wireless Wizard"it repeatedly indicated it could not make the wireless computer connection, and it was hung up for a long time "checking my computer' The wireless appears to be working OK, but I can not find a way to make the wireless network secure with a password. What do I do?