Open a door with a smartphone and an arduino uno

I want to build my own house control system with an arduino, but first it's enough to open the door :slight_smile:
I want it like that:
I have an arduino uno with an ethernet-shield connected to my network at home (Fritz!Box).
When I am in this network with my phone, I should be able to open the door with my smartphone via an android app that I have programmed. Can anyone please explain, how I can connect my phone to the arduino via Wifi/Lan

Thanks for answering,

PS: Please excuse my bad english, I am 14 years old and german.

You can create a simple webserver on the Arduino that your phone can connect to with a browser to change the state of an LED. Once you have success with that, you can change the state of the door, as well as the LED.

There are a number of examples on the Arduino Playground that explain how to use the Ethernet shield to set up a webserver.