To couple the wrenches together you need to put the box end of one wrench on the bolt you want to turn and then slide the box end of the other wrench into the open end of the other and they will kind of lock together. A picture would surely be worth a thousand words here but I am sure that if you have half a brain you can figure it out by simply playing with it for a second. Remember, box end into open end and lever it all together.

Personally I recommend a long 3/8" extension and a wobbly socket. It is much faster and safer. Make sure that you disconnect the battery first or you may find your self doing some arc welding when you take the cables off of the starter.

Mark