Hi there. You can simply add items to the navbar of your Tribe community as explained here: https://community.tribe.so/question/5ca777abe0bdb361793168c811
We suggest to use the same items you have in your main website, but it totally makes sense that some of the items from your main website shouldn't be in your Tribe community. Follow the instruction provided in the link above to simply customize your navbar.
There is no automated way to insert all your website navbar into Tribe navbar, as it can cause lot's of trouble for many portals, becasue they simply do not want all the sections from their website to be in their community too.