Help with my SD card reader?

i had recently purchased a Dynex card reader so i can put pics from my digital camera to my imac,problem is that nothing happens when i connect this product. so i called the company and they said i dont need to doownload a driver,even though on their website it has a driver download for macs,and once i downloaded it it says the file is a text file with the last three initials .sit, what should i do to open that setup up