"My opinion would be that it is every teacher's best friend," she said.
Miller is able to post or buy everything from lesson plans to activities she's done in her classroom and share with them with 4 million members to earn money.
"You're taking everyone else's activities and changing them to make them your own, and puttng them into your classroom to give your children -- your students -- the best educational experience possible," she said.
Miller said she's been selling her activities for four years. During that time, she's made a total of about $4,000.
"Teachers work really long hours, and therefore it's nice to get an email that says, 'Hey, you just made $15 today,'" Miller said.
The website takes about 40 percent of the sellers' profits, unless they pay to become premium sellers. Miller pays $65 a year to be a premium seller and keep 85 percent of her sales.
The useful tool was recommended to her by another teacher. About two-thirds of the school's teachers have used it.
"It's a nice little resource for teachers if you're in a funk or if you want to do something but you just can't come up with something fresh," Miller said. "It just gives you some great ideas."