Both of these words refer to people who work at a company - but staff is always singular and uncountable - it describes the entire group of workers as one thing. Employees is plural and countable - it describes the collection of individual workers.
The entire staff was happy about the extra day off.
All the employees were happy about the extra day off.
Note that "staff" takes the singular verb was, and "employees" takes the plural verb were.
Whenever you use a specific number, use employees or staff members:
Lucario is a species of Pokemon in Game Freak and Nintendo s Pokemon franchise. Lucario first appeared in the film Pokemon Lucario and the Mystery of Mew were it was the central character. It then appeared in, Pokemon Diamond and Pearl , the video game and in its subsequent sequels. It also appeared in various spin off titles, merchandise and both in printed and animated versions of the franchise. Lucario is voiced in Japanese by Daisuke Namikawa and in English by Bill Rogers. It is one of more popular Pokemon from the fourth generation. It has earned a spot in the brawl and is a popular choice in the battling arena. It has the skills to be a physical or a special sweeper.