Ssam means "wrap" in Korean and refers to a variety of little hand wraps. Sangchu ssam is lettuce wrap and is often served alongside Korean BBQ (kalbi and bulgogi), but can also be offered with sengsun gui (grilled fish) or samgyeopsal (3 layer pork). There is no strict definition of what goes into a sangchu ssam, but typically one might add a piece of meat, a little bit of rice, some sauce (see below) and maybe a slice of kimchi or green onion salad.
Wash the red leaf lettuce thoroughly and break apart into individual (whole) leaves. Pile onto a plate. Peel garlic and grill alongside your meat (if you are grilling).
If you want, you can make a green onion "salad" but slivering them thinly, then dressing them in a mix of soy sauce, rice vinegar, sesame oil, hot pepper powder and sesame seeds. Serve in a low bowl.
To make a lettuce ssam, take a piece of lettuce and place a piece of meat (any of the above). Put a daub of sauce -- ssamjang (wrapping sauce) or plain gochujang (red pepper paste). You can add a whole peeled garlic piece (grill these along with the BBQ to reduce their spice) or pieces of the green onion salad. You can also add a little bit of rice, or some banchan (side dishes) like kimchi. Finally, wrap it up and stuff it into your mouth!