There's a relationship between voltage, resistance and current. First discovered by Georg Ohm, the law that carries his name defines that and increase in voltage across a resistor results in an increase in current through it, and decreases in the same proportion as an increase in the resistance through which it flows.
This is translated to the mathematical equation I = V / R
From this equation, others defining voltage and resistance in terms of the remaining properties of the circuit can be derived:
V = I R
R = V / I
These form the basic equations that when combined with other properties of circuit, which you will find in a later lesson, form the basis for all circuit analysis and design of electric and electronic circuits.