How to connect multiple i2c-interface devices into a single pin A4 (SDA) and A5 (SCL) on Arduino?
Some folks are having a hard time visualizing things connected together, so here's a picture:

(Serving suggestion)






simulate this circuit &ndash; Schematic created using CircuitLab
I2C is a bus, so like-named signals are connected together.   The addressing scheme allows the microcontroller to select which device it's talking to. On the Arduino the 10k pull-up resistors goto "VDD", which is the 5V or 3.3V pins.