A discovery is when a person comes to realize something that had been present for quite a long time .One can only discover something that had been existing for long.Its just that people did not know about it earlier.
For example: Isaac Newton discovered gravity.
An invention is giving the world,the people,something unique,something that did not exist before which helps them in many ways.
For example: Samuel Morse invented the telegraph.
If you find something which is already present in the world , it is discovery... If you create something new and introduce that to this world, it is invention
The basic rule of thumb is that a discovery is something which already exists, whereas an invention is something which has been created as being entirely new.
So for example, America was discovered (probably by the Vikings in the 10th or 11th Century). America existed and so it could not be invented. It had to be discovered.
On the other hand a chocolate bar could be invented. So although the peoples of Central America may have known about the cacao trees for hundreds of years, they were 'discovered' by Europeans, who brought back the cocoa beans from Central America. These beans were then made into the same drink as had been made in America for years, again a discovery. However, when the Europeans found new ways to grind up the beans and mix them together with sugar and cream or milk, then this created chocolate and so this is an invention !
A discovery is when someone discovers something. Invention means when somebody inventes something.
Suppose you had married with a woman. That means you discover a woman and after a year that woman give birth to a child this child called invention.