Place upper strap (with D-ring) around your dog's neck. Place lower strap (with buckle) around dog's chest and place dog's left leg through the loop. Adjust lower straps to fit comfortably and fasten buckle on the side. Now you can attach a leash to the silver D-ring.
Petco 3/8" Black Single Ply Nylon Adjustable Dog Harness
Size: Small
Dimensions: 3/8" Width
Pet Size: For Chests 10"-18"
Petco 5/8" Black Single Ply Nylon Adjustable Dog Harness
Size: Medium
Dimensions: 5/8" Width
Pet Size: For Chests 14"-24"
Petco 1" Black Single Ply Nylon Adjustable Dog Harness
Size: X-Large
Dimensions: 1" Width
Pet Size: For Chests 22"-38"
Petco 3/4" Black Single Ply Nylon Adjustable Dog Harness
Size: Large
Dimensions: 3/4" Width
Pet Size: For Chests 18"-30"