Use an apostrophe before an s to indicate the possessive or ownership.
For example: Durham College's 40th anniversary was September 18, 2007.
When a noun ends with an s, use a single apostrophe after the s.
For example: The School of Health & Community Services' professors are qualified professionals with years of real-world experience.
Plurals of decades do not require an apostrophe.
For example: The use of technology exploded in the 1990s.
Do not use an apostrophe with the possessive pronoun its.
For example: Your Student Association had its first meeting of the year.
Use an apostrophe for the contraction meaning it is. It is becomes it's.
For example: It's cold today.
Use an apostrophe when referring to dotting the i's and crossing the t's.