Resistance

for a certain applied voltage the current which will flow in the circuit will defend on the opposition of the circuit to current flowing through it. This opposition is called the resistance of the circuit; the unit of resistance is the ohm.For Radio purposes the ohm is rather a small unit and multiples are commonly used.
1 kilo ohm= 1000 ohm
1 megohm=1000 kilohm or 1000000 ohms

we may cosidered the voltage as being equivalent to the pressure in water system; the current as the being flow of water and resistance as the friction of the pipe to the flow of water.