The sheet bend is used to tie two lines together. It is perhaps the most generally useful knot of all. When used to tie a line to itself, making a loop, it is called a bowline.
The strain is taken on the ropes in the middle - not the one coming out the side.
How the knot is made is not critical - it is the final shape that is important. One can make the flat loop first, and work the other rope around it. Or one can make the crossed loop first - required when tying a bowline.
The two images show front and back views of the same knot
Easy to make
Easy to undo when tension is removed
Does not easily capsize
Hard to make under load
Dangerous to make under heavy load
Joining two equally-sized ropes
Extending a towline or stern line
Method 1: the same as a bowline
Method 2: starting with the flat loop