NOTE: If none of the following work to resolve the problem, since the tablet is brand new, I would suggest taking it back and getting them to exchange it for another one.
1. Try and restart the tablet. Sometimes it is that simple.
2. Update the firmware and any apps that need updating on the tablet.
3. If the problem persists, check your time and date on the tablet to make sure it is correct.
4. Should none of the former work...
a. Clear out the WiFi data on the tablet.
b. Reboot the modem/router.
c. Once the modem/router is fully 'up' again, reboot the tablet and re-input the WiFi data.
5. Check your internet connection. It may be what is going in and out rather than the tablet.
6. Make sure you have "Data" turned off on the device when using "WiFi" (that is if you have a plan with data through your tablet). If you don't make sure it is turned off, the device can keep trying to switch to "Data" when you try and use "WiFi".
7. Now, if you are still having the problem at this point, and you are sure it isn't the modem/router that is the problem. Then you may wish to try a "Hard Reset" of the device. However, I really suggest saving this as a last option (or last before parts repair/replacement).
NOTE: Doing this will clear 'all' the data on your tablet, so it is suggested you not choose this option unless you have to, or aren't worried about losing anything on the device.
Be sure you back up any data you want to keep, to a computer or cloud account, before doing the reset.