Re: Wifi Issues
Can you connect to a device in your home network? Say try printing a test page while on WiFi and connected to the extender. This will help narrow down what may be going on.
There's a built in tool called Network Utility. You can find it by searching in Spotlight. Once Network Utility is open, go to the Traceroute tab. Enter an address for a news or shopping site - something that will require the Mac to go outside of your home network to get the web pages. See if the Traceroute travels beyond your router's gateway. Most gateways are configured with a .1 at the end of the IP Address. Something like 192.168.1.1. You can find out your gateway address by using the Netstat tab in Network Utility, or in the Network Preferences/Advanced.
If the Traceroute make it out of your home network and onto your ISP's network, then you know something is going on outside of your control. If the Traceroute doesn't go all the way to say, www.androidcentral.com and complete the Traceroute, don't worry. Sometimes networks block the "ping", or ICMP protocol at certain points in their networks. That's fairly normal. The key thing is if you can get out of your network and onto your ISP's network.
The other thing to check is for DNS. DNS helps to resolve IP Addresses to friendly names like iMore | The #1 site for iPhone, iPad, Mac, and all things Apple!. If DNS is not available for your Mac, that could cause problems when trying to reach websites. Check to see that you have DNS setup and available in the Network Preferences/Advanced.
Another option to try is to tether your MacBook to your iPhone and see if you can get to the internet that way. If your MacBook connects to your iPhone, get's an IP Address and can go to websites, then that could indicate you have a configuration or other issue in your home network.