How to multiply two columns in Excel

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.

You can use a formula: =a2*b2 and fill down that column. Or =a2*0.2 , may this will help you out.

Just follow some steps for doing this, =(first column*second column) and than press enter, this is a proper way of doing this, after writing this you can drag and drop and get the answer of other columns too.