There are different batteries with different charging systems. For example, older DJI drones only worked with the brand's proprietary chargers.
Generally speaking, equip yourself with the original charger of the brand of your drone, then plug this charger into a power outlet. Remove the battery from the drone. Then, plug the battery into the charger. Be careful, it is also possible that the battery is integrated into the drone and does not need to be removed.
Yes, the more capacity you increase, the more autonomy you will have. However, this also means increasing the volume of the battery. The drone will therefore be heavier and may not support the load.
It all depends on the system and the charger. Some fast chargers will charge the drone in 2 hours. While other conventional chargers will require up to 6 hours to recharge the battery.
This is a good practice to best optimize battery life while maintaining the best performance for your drone.
If it's for old DJI for example, we don't really have a choice. Chargers are exclusive to the devices. For models and other brands, universal batteries are compatible.
You will just have to be careful to have the right voltage for the drone you own.
You should know that the autonomy can be increased depending on what the model can support.
Generally, a drone can fly for at least 15 minutes. This flight time can go up to 45 minutes depending on the battery capacity.