Conducting wires oppose the flow of electric current, this property is called resistance. This phenomenon is sometimes a drawback (when you wish to transport electrical energy, for example), but sometimes it is an advantage (as when it is used to produce light with the filament of a light bulb).
Some resistors are designed to be used in printed circuits and the value of their resistance is printed on them using a colour code. A resistance like the one in the picture is equivalent to many metres of wire. Resistors are ceramic cylinders covered by a conducting film with axial wires on both sides.
electrical resistor

You can create a variable resistance by making a coil with many metres of wire on a spool and placing a mobile brush on it. You can get more or less resistance by moving the brush along the spool. Carry out the activity suggested in the following visual to understand what a variable electrical resistor is. 

Licencia de Creative Commons Licencia Creative Commons Reconocimiento-No Comercial-Compartir Igual 3.0 España
logo INTEF Ministerio de Educación, Cultura y Deporte