The definition above is quite a mouthful, it simply states that the current passing through a conductor increases if you increase the voltage.
Obvious really - increase the pressure (voltage) and you will find more current will flow.
All circuits have a certain degree of opposition (resistance) to current flow through them, the relationship is given by R=V/I.
An increase in current flow with the same voltage will assume an decrease in resistance
The above triangle allows the student to calculate any of the 1 of the 3 variables if the other 2 are known.
Cover the variable that you require and perform the resulting calculation.
Consider the circuit shown below
The resistance of that circuit would be given by R=V/I 24/2 = 12 ohms
The current flowing through the circuit would be given by V/IR 24/12 = 2amps
The voltage would be given by I x R 2 x 12 = 24 volts
If you continue your studies to a more advanced level than GCSE then you will find that ohms law is one of the most fundamental electronics laws