Custom hooks is not different things it is as usual same thing as it normal hooks like useState and useEffect use as common mrthodology to implement their code in best possible manner such that, it's implementation is mostly used in fetching an api ,
we can also use existing hooks in our custom hooks such that it can be most popularly known as Custom hooks
in Reactjs during creation hooks we have have to take care of following conditions
1. the user must have to consider it as a callback function
2. there is no any restriction that you can not use any builtin hooks
3. it is not only use for fetching API but most of the time it uses as,