"I possess two years of administrative experience."
However, this is a rather difficult question to answer because it really depends on the format of your resume. Usually, a resume includes the dates worked at a particular position. Under the position, one would describe the type of work that position required. For example,
Bought merchandise for two different gift stores.
Directed daily store operations and sales.
Directed merchandise presentation, inventory control, and customer service.
Scheduled and supervised a 7-person staff.
Increased sales volume 22% more than corporate projection.