One goes under the forearm/forend; be careful not to allow the swivel stud to touch your "sandbag".
The other "sandbag" goes under the stock nearest the butt plate (careful not to allow the swivel stud to touch your "sandbag").
Keep both of your arms on the bench/table & stay "in the scope" after the shot and get back on target immediately (called the follow through - most important IMO).