What one can do to calculate the unit price is to look at for example the weight of the item (for example if it is a grocery item like a package with tomatoes) and do the following division:
Price of the item / weight
if the price was for example $5 and the weight of the tomatoes was 4 pounds, we get the following unit price:
$5 / 4 lb = $1.25 per pound.
We know that way how much we are paying per pound of tomatoes.
Is this example clear enough for the understanding of the unit price?