I used the following request link to extract data from the Stack Exchange API. But I have no idea how to create "filter" as used in the request line.

Please help me understand the creation of such filter in order to get the desired fields in response the response.

https://api.stackexchange.com/2.1/users/2/answers?key=xTr7YgsHdmfcevW6Vo1*BQ((&page=1&pagesize=100&site=stackoverflow&filter=!3u0zcO%28lpHVEGuskA