After setting up the BLTouch in firmware, you need to activate the leveling function for every print by inserting the leveling G-code 'G29' in the start G-code script of your slicer. The code should be placed directly after command
Note that you can test the working of the sensor from the printer display: sensor can be deployed, stowed, reset and tested.
An alternative is to use the
M500 command once in a while (for beds that don't change, don't get handled by excessive force and/or are operated at the same temperature) or store the shape of the bed through the display interface and put the command
M420 S1 in your start G-code instead.