A staff is a group of workers. In particular, this word is used for offices, restaurants, hotels, hospitals, schools, and organizations. Although the word "staff" refers to members of a group, in American English this word is usually singular; in British English, it’s plural.
The staff at that company is threatening to quit. (American English)
The office staff are away on vacation. (British English)
The company has a very large staff.
The administration is meeting with faculty and staff. (faculty = teachers; staff = office workers and support)
A cafeteria is available for hospital staff and visitors to the hospital.
They need to find an office space for a staff of over 100 people.
Several new staff members need to be trained on office software. (This sentence uses "staff" as an adjective.)
This company has a small staff.
When the word "staff" is used as a verb, it means to put people into positions: