Regarding the path of storage of file?

Hello.

1.where the file will be stored ?

I think it is output to RDS storage.
RDS itself is a managed service, so I don't think you can connect directly to the OS and access log files directly.

2.do we need to create a separate storage path for it or else it will be stored in RDS console or S3 bucket?

I don't think you can change the file path etc. as it is a managed service.
I think the storage location is within the RDS storage.
https://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/USER_LogAccess.MySQL.LogFileSize.html

3.could you provide the neccessary steps for viewing the file once enabled?

You can view the logs by following the steps in the document below.
https://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/USER_LogAccess.Procedural.Viewing.html

It is also possible to output to CloudWatch Logs.
https://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/USER_LogAccess.MySQLDB.PublishtoCloudWatchLogs.html

4.Does it occupies more storage capacity?if yes ,any alternative ways for them ?

I think it uses storage capacity because it is stored in RDS storage.