JMP(04) is always used in conjunction with JME(05) to create jumps, that is, to skip from one point in a ladder diagram to another point. JMP(04) defines the point from which the jump will be made; JME(05) defines the destination of the jump.
When the execution condition for JMP(04) in ON, no jump is made and the program is executed consecutively as written. When the execution condition for JMP(04) is OFF, a jump is made to the JME(05) with the same jump number and the instruction following JME(05) is executed next.