I am a beginner at this. Using Excel, all I want to do is to multiply 2
columns  together to give a third column. For example, a list of numbers in
column A against a list of numbers in column B to produce a column C - (A2
times B2 to equal a number C2))  

or to multiply all the numbers in one column (like "calories" or A2-A18)
times one number (like 0.2) to produce a third column. I tried to do this but
the results replaced the numbers.  

and to multiply one column times two other numbers.

I'm going nuts (I'm swearing all over and I don't usually swear) trying to
add numbers for a book I'm writing. I've got macronutrients like protein and
I want to figure out how many calories the protein is by multiply the number
of calories (in column A) times 0.20

I would do this by calculator but I've got about a zillion numbers and last
time I tried it I made too many mistakes.

Thanks to anyone who can help.