I thought the reason why the seasons changed was because of the earths tilt and the atmosphere. Is that true?

Hi, msjones1228!

There's a lot of information available out there on the Internet concerning what you're asking. So much so, that copying and pasting information here would not be warranted.

Have you tried the following sites?

SPACE.com -- Summer Solstice: How and Why Seasons Change

Seasons (Science U)

Reasons for the Seasons

HowStuffWorks "What causes the seasons?"

Seasons of the Year

Thanks!