How do I set the colour of a cell depending on a value in another cell?

Use the "formula is" option under Format, Conditional Formatting

i.e =C3=4 will set the condition to format the cell you want coloredif the value in C3 is equal to 4. You may also use greater or less than. for the condition

:i.e I tried to use the conditional formatting suggested but it did not work. Is there other steps that must be done to make this work as per the original question?