Fridges use electricity to move heat (they don’t make or absorb heat)
So the amount of electricity used depends on how much heat has to be moved, and how efficient the mechanism moving that heat is.
Fridges use a refrigerant, pumped by an electric pump. They try to keep the temperature in the fridge at a constant low temperature (say around 3 degC typically). When you put a new item in the fridge first that item must have heat removed from it’s mass (assuming it was hotter than the fridge temp when put in) and then all the fridge has to do is to take enough heat out of the cold box to compensate for the heat that leaks back in from outside (which of course depends how hot it is outside the fridge)
The reason new fridges are less costly to run than old ones is because they are better insulated, so less heat leaks back in and has to be taken back out again! Often old fridges are actually more efficient in terms of heat moved per unit of energy consumed because they use refrigerants that are more effective (but now have been banned for being really pretty nasty to the environment)
What this means is that the amount of energy your fridge uses over a short period may not reflect its average consumption over a year. Depending on how hot it is in your kitchen, when you last put a load of warm things in to cool down, when the door was last opened etc, short term measurements can be way too high, or way too low!
The final clever bit about fridges is they are more than 100% efficient in terms of the energy they required to move heat. Because they are not heat convertors, but just movers, they typically have an efficiency of around 200 to 300 percent. ie, 1 joule of electricity can move between 2 and 3 joules of heat!