Q: my new mac is running very slow

If it's less than 14 days old return it for an exchange, if it's less than 90 days old or if you have already bought AppleCare then call AppleCare today. AppleCare gives you 90 days of free telephone support or if you already bought AppleCare (strongly recommended) it will extend the warranty to 3 full years and provide telephone support too.

Learn how your computer works here, perhaps you purchased the under powered budget model.

Why is my computer slow?

Even a budget 2012 iMac has a great deal of power, exactly what do you mean by under powered?

Once you contact Apple's Express Lane and sort out your current issue, see:

Mac Maintenance Quick Assist,
Mac OS X speed FAQ,
Speeding up Macs,
How to Speed up Macs,
Macintosh OS X Routine Maintenance,
Mac troubleshooting: What to do when your computer is too slow,
Essential Mac Maintenance: Get set up,
Essential Mac Maintenance: Rev up your routines,
Maintaining OS X, 
Five Mac maintenance myths and
Myths of required versus not required maintenance for Mac OS X for information.