Subscripts are the tiny numbers. They show the number of atoms in that element. Coefficients show how much of the compounds there is.
On the reactant side there is 1 carbon atom because there is only 1 C on the left side. There are 4 hydrogens because the subscript (tiny number) shows a 4. There are 4 oxygen atoms because there are 2 sets of O2. 2*2=4.
On the product side, there is only 1 carbon atom because there is no subscript or coefficient. 4 hydrogen because 2*2=4. 4 oxygen because there is 2 oxygens in CO2 and 2 in H20. 2+2=4.
Basically multiply the subscript next to the element by the coefficient to find the number of atoms. I hope this helps you.