You can separate the troubleshooting into parts. Go to a place having a wi-fi internet hot-spot, like Starbucks or Gloria Jeans'. Assuming you are in the USA:
Get a coffee and turn your tablet wi-fi on. From
1. Go to Settings > WIRELESS & NETWORKS > Wi-Fi, and slide the Wi-Fi switch to the ON position.
2. The device will scan Wi-Fi networks automatically and display the available names.
• If the device finds a network that you connected to previously, it will connect to it automatically.
3. Tap a network name to connect to it. Tap 'Agree to conditions' if necessary.
You should then be able to go to a webpage. Once you get this bit working, you can turn to your home internet.
You need of course an account with an ISP, who will probably supply you with a gateway (modem/router). If you only have a modem (connection box to the ISP) that does not have a wi-fi capability, you will need to get a router (wi-fi broadcaster). These can be quite small and neat.
For assistance on this contact your ISP tech help line, since some of the advice is peculiar to the equipment they use.
Connect the router (if you needed to get one) to the modem with an ethernet cable
and follow the setup instructions that came with it. Then do the same as in the cafe wi-fi hot spot. It should work.