You can either add a new Wi-Fi network from available networks on your Galaxy Tab, or you can also add a new Wi-Fi network manually. So, in following you will find the method how to connect to a Wireless network on Galaxy Tab.
Connect to WiFi on Galaxy Tab
On “Home” screen, tap “Menu” and then “Settings”
Then navigate to “Wireless and network” > “Wi-Fi settings”
Check mark the box followed by “Wi-Fi”, to Turn it ON
Find available networks under “Wi-Fi networks” section tap on that and connect, if WiFi network is secured then you need to enter its security key first.
Now you are connected to the internet and enjoy browsing and other web tasks.