If you use soft baits for fishing you normally tie them with an open loop to your trace.
This will allow the lures to move freely.
Soft baits are supposed to immitate a wounded fish in the water.
A Uni or Clinch knot can not be used here, cause then the lures would be fixed in place.
The Lefty's Loop Knot and the Rapala knot (both very similar) are important knots, that are used for soft baits.
This video tutorial explains how to tie the Rapala Knot
If you were wondering how to rig a soft bait onto a worm hook check out this tutorial.
Texas Style Soft bait rigging ;-)
Yet another good tutoial of how to rig soft baits onto different jig heads ( lead head hooks ).