I'm pretty new to this website so my knowledge about wifi shield or xbee internet gateway (whatever that means ) is very little.
I want to be able to control my garage door from anywhere as long as I have internet connection. I would like to control it with my smartphone. So far, everything I found on this forum is either way too complicated for my newbie mind or doesn't relate much to my need. Any tips on where to start, materials I will need or articles online to help me?
You need to expand on what you want to do with "control" the door. If only open and close, al you need is a relay to parallel the indoor push button. Easy for an Arduino to do.
That is quite a big first project . I would break it down into a series of smaller projects that help you learn as you go, before trying to join them all together to make the final project.
So for your project, you should undertake some smaller projects to understand:
wifi shields and a simple web server on the Arduino to accept commands and cause something to happen on the Arduino
sensors to detect whether the door is currently open or closed
digital outputs to cause things to happen on other devices. The exact nature of this will depend on how your garage door works
websites and security
The above is not an exhaustive list, just something off the bat to get you thinking. Don't forget to think about security, as if you can open your door from anywhere then somebody else can as well .
For the first item on davidrh's list, consider the ESP8266. It is a WiFi module with a pretty fast and powerful processor. The ESP can be programmed using the Arduino IDE after installing the Ardduino core.
No, seriously, this is like leaving your front door wide open. IOT devices can be hacked extremely easily, especially if you're a beginner with little to no knowledge of Internet security.
I would never install something like this myself.
Is it worth trying, in order to learn more about electronics and IOT? Absolutely! Should you actually connect it to your garage door? I don't think so.
BTW, the ESP8266 that groundfungus suggested is an awesome chip, I'd really recommend to check it out!