Problem with multiplying cells automatically

Hi, Iam new to this forum and new to Excel as well. This is my Excel problem:

So, I have an commercial invoice in Excel filled with data. The thing I want to do is to somehow automatically multiply/divide the value from E5 with D5 in a blank cell H5. That is what I want to do to the end of the invoice (the next situation would be to multiply for example E6 with D6 in H6) to the bottom for each field. What I exactly would like to do is to set a formula or anything what is possible in Excel so this can be calculated automatically for each cell to the bottom.
Any help, tips, recommandations would be appreciated.
Tnx in advance.