hey fellow authors! Im a young writer and ive been told that you should put two spaces between each sentence. I never see that in book I read, so it that necessarily true?

Huh?! Really?! Am I supposed to too? Oh I really want to know the answer myself now....eeek! I'm so not helpful, sorry XXX

I don't think it's true
And if you say you haven't really seen it in an actual book then I guess it is unnecessary.

>>1 This is a convention from when people used typewriters. It's no longer common, but is still in use. For example, you can set Word to expect either one or two spaces after a period. Don't bother with two spaces though, unless you're writing a paper for school and you're stretching to fill a page requirement :P

I've just sent my book off to an agency and there was nothing in the submission guidelines about adding an extra space between sentences. I don't think you need to.
II think some agents/editors ask for double spacing between lines though. Could you have misheard?