A quick video about using E27 to AC socket adapters to convert your lamp socket to an AC outlet.
These adapters usually have pretty low ratings, for example 2A 250V maximum. You should remember that most lighting circuits are not designed to handle high current so you should only power small appliances through these adapters.
You risk tripping your breaker switch, damaging your wiring or even starting a fire by plugging high current appliances into this kind of adapter. Also note that there’s no support for a ground pin.
These adapters have many uses, for example when traveling and staying somewhere that has no outlets or poorly placed outlets. Or around the home where you may need an outlet in an awkward location, like to mount and power a security camera for example.