A geometric progression is a progression in which there is a constant ratio between terms. The value found by dividing any term by the term before it gives you the constant ratio.
What is the next number in the progression 1, 2, 4, 8, 16, … ?
The ratio is = because . You could also have said that you're simply doubling each number to get the next number. So doubling the last number, 16, gives 32.
What is the next number in the progression 3, 9, 27, 81, … ?
The ratio is because . You could also have said you are multiplying each number by 3 to get the next number. So multiply the last number, 81, by 3, which gives 243.