The complete link for an Ebay item can be as short as this : http://www.ebay.co.uk/itm/172192184368
Which Arduino board do you use ?
In the middle you see GND and HV on one side and GND and LV on the other side.
The GND's are connected.
Arduino side : 5V to HV. GND to GND. There are four channels, but only two channels are needed for SDA and SCL.
Sensor side : 3.3V from Arduino or from module to LV. GND to GND, the other side of the selected channels to SDA and SCL.
If the sensor runs at 3.3V, you need to get 3.3V from somewhere to make the level shifter work. That is preferably the same 3.3V that the sensor uses, but if that is not possible, then you may get that 3.3V from somewhere else.
Some level shifters have a 3.3V voltage regulator on the board, but this one has only the 4 mosfets.
If your Arduino board is a Pro Micro (without 3.3V output) and your BME280 module has no 3.3V output, then you should get a 3.3V regulator as well, or get one of those level shifters with 3.3V regulator included : http://www.ebay.co.uk/itm/141742393893