how to create folder on BitBucket?

Bitbucket has now Projects feature which enables to organize repositories hierarchically just as you describe. The URL does not reveal project, but in web you see them.

BitBucket does not provide you with such a feature to add an folder and manage your repositories inside a folder. Once you are in an account you can keep adding repositories, but you cannot manage repositories inside your account in folders.

Figured it out,

Open Repo >> Goto Source >> + New File >> Under fileName:

folder1/folder2/file.extension

Go to source and click Add File. Then at the filename, first write the folder name, a slash (/), and the file name. E.g.,

folder/file.php

This will automatically create a new folder if one doesn't exist. This would be named with the folder, and the file.php will be inside of the folder.

Goto Source >> + New File >> Under fileName:

folder1/folder2/file.extension