Explanation of when to use the prepositions for, while and during.

FOR
Use 'for' with a period of time to express the duration or 'how long' something has happened:

• for three weeks
• for many years

WHILE
Use 'while' plus a verb form:

• while I was watching TV
• while I lived in New York

DURING
Use 'during' with a noun to express 'when' something happens:

• during class
• during my vacation
• during the discussion