Butt (heat) fusion is the most common among techniques.  The two pieces of pipe are aligned.  The facing blade is set into place and shaves both ends of the pipe so they will have a true union.  Once this is done the heat plate is dropped into place and the pipe is pressed up against until there is a bead formed on both pieces of pipe.  The heat plate is removed and the pipe is pushed together and left to cool, then on the next joint.