Adding images

Sorry i feel like an idiot for asking and feel free to delete if this already exists on here somewhere or if it just doesnt belong up.

But how can i add screenshots to a post to show what im trying to ask/explain. I know theres an insert image button but it wants a link to a URL but its stuff from a powerpoint so i just have a screenshot of it, i dont have it online anywhere. Wondering if it's possible to just add images or if i have to do something else. 

Thanks