As a newbie I found the online guide painful to follow for setting up a wireless bridge.
I wrote a script that automatizes this. I have tested it with openWrt 18.06.1 on a Linksys WRT1900AC v1.
The script is self-contained: it's a user-guide for setting up a wireless bridge and a script that actually does it.
If you want to learn how to set up a wireless bridge with openWrt, just run
In a nutshell: install openWrt, copy ./openwrt-setup-wirelessbridge.sh to the router and run it
On the GitHub repository you find a minimized as well as a just-do-it bare version.
Hope you'll find it useful