* to use drowns is good for us because that can do many thing
⇨ it's convenient for us to do what we want
* that can ⇨ they can
* when disaster happen ⇨ when a disaster happens
* learn well about them and understand well
⇨ learn and understand them well
I think that [drones are useful] because they can do many [things]. For example, they can take [pictures] in dangerous places when [disasters] happen. So we should learn [and understand more about them].