Wormholes were tunnels through spacetime that could transport objects to other places. They had strange time dilation effects that caused temporal anomalies.
In the episode "RD: Backwards", the Boys from the Dwarf travel through a wormhole that takes them to a version of Earth in the early 1990s - but time is running backwards. This wormhole was likely a remnant of Holly's failed attempt to get them home in the previous episode using the Holly Hop Drive.
The escape pod that Rimmer used to flee a Simulant Battle Cruiser was designed to locate the nearest S3 Planet. It detected a suitable planet on the other side of a nearby wormhole. The time dilation effects inside the wormhole caused time to pass more swiftly for the traveller. The upshot of this effect was that Rimmer experienced 600 years on his new home planet while he waited for Starbug to catch him up. (RD: Rimmerworld)
When one version of Ace Rimmer died aboard Starbug, he left instructions for his lightbee to be placed in a special coffin. Starbug followed the coffin through a wormhole to a planet whose rings were made up of millions of identical coffins. (RD: Stoke Me a Clipper)