A softener loop is simply an access point, usually in the main water supply line before it gets to the WH or any other usage point. By cutting into the loop, the softener is simply inserted "in series" with the water flow. One technicality is that the softened water should NOT be fed to outside hose bibbs. Sodium softened water will cause plant leaves to turn yellow.
As far as the drain, most softeners use something like a 3/8" ID vinyl tube. This must be connected INDIRECTLY to the drain system. It must (a) be connected via an air gap, and (b) of course it must connect to a trapped entry point. One common connection is to drain it to the washing machine standpipe.