size and shape of the plug that goes into the laptop and the charging port on the laptop
voltage & amperage: the chargers output voltage must be the same, the amperage must be equal or higher but never below the required amperage otherwise stuff starts to get warm and may potentially get too hot
read your laptop chargers label
Or if you don’t have a charger read the laptop specs
It’s recomended you get a manufactory one that’s made for your laptop which you should be able to Google, make sure you’re not getting fake chargers either because those can cause house fires