Typical example: https://www.google.co.uk/maps/@50.9997356,-0.9166437,14.25z?...
More complex example: https://www.google.co.uk/maps/@51.1101752,-0.1713974,7297m/d... . Note the M23 on one side, Crawley Avenue on the other, and Peglar Way right in the middle. All of them serve to route traffic around the town centre instead of through it.
In many cases you can see how the original through-road (sometimes dating back to Roman times) had the bypass patched on; without the bypass the "High Street" would have been a stroad.
(Fans of The Hitchhikers Guide to the Galaxy may recall Arthur Dent's cottage being demolished to make way for a bypass. This was an issue: the nature of bypasses meant that building them often required the demolition of nice little cottages on the outskirts of small towns.)