A self-assigned IP address means the computer is not getting an IP address from your router.
First thing to do is reboot both your router and your computer (maybe even your modem). If you still have issues, then try creating a new Network location or create a new admin user so you can test your connection to your router using default or newly configured settings. Try using an Ethernet cable for a direct connection to your router to eliminate any possible WiFi issues.
See these two Apple articles for troubleshooting networking issue & WiFi issues:
Using Network Locations:
https://support.apple.com/en-us/HT202480
WiFi Issues:
https://support.apple.com/en-us/HT202663