Can your phone connect with wifi elsewhere, like at the local coffeehouse? If not, then your phone has a problem, and I would suggest rebooting it. If your phone can connect elsewhere, then presumably the issue is with your home wifi.
Things you can try:
1. Reboot your phone.
2. Reboot your router (unplug the power, wait 10 seconds, plug it back in, and wait another 20-30 seconds for the connection to reestablish).
3. Make sure your router's firmware is up to date. You can find updates on the router manufacturer's website.
4. Change your router's security (e.g., from WEP to WPA, or from AES to TKIP).
5. Try turning off your router's security altogether, to see if it's the security that's causing problems.