The Loop to loop knot is used for joining two pieces of line together, usually mainline to hook link. One advantage to using loop to loop connection, is the hook line can be easily changed.
Most ready tied hook links have a loop in the end for easy attachment to the mainline.
How to tie Loop to loop knot
Take the loop from the mainline and pass through the loop on the hook link.
Pass the hook through the loop on the mainline.
Once looped together the knot should look similar to a reef knot.