"Sharing" is an selfless act which involves giving some of what is yours to someone else, such as a friend or someone less fortunate. However, the difference is that even though you gave part of something to someone, it's still in fact yours. There is a difference between sharing and giving;When you give, you don't have that thing anymore in its complete form. When you share, you usually give someone half or a little of something. So, when you give someone one half of your sandwich, that person will have that entire half-sandwich to himself. He can eat it all if he wants. If you are sharing with that person, then the sandwich is still yours, but you are giving your friend permission to have some of it. A good comparison here would be like a guest at a house.

You can use the word share for a noun which is used or eaten by more than one person. But the verb to share needs an object. We share a bathroom.. We shared our lunch. We share our work.