Actually, while setting up additional users is simple enough, and you can grant certain "privileges" to them via the panel, your desire to share directories with those new users is not so simply accomplished.
You might start by checking out this DH WIki Article on "How Do I Share Website Access WIth Another FTP User?".
While there are workarounds you could experiment with, involving the creation and management of *nix style groups, they are rather complicated, non-intuitive, and a general PITA to manage for most.
I prefer to accomplish this using CGI scripting. This allows the user to upload the files, but allows me to retain ownership of the files. Many CMSs (Content Management Systems) allow this functionality, and there are other ways to allow users to contribute to your site (and manipulate files in your directories). This works especially well on DH because of DH's use of suexec, which allows CGI to to run as your user, rather than as a separate user for the webserver.
I highly recommend ffileman, which is a "free" perl-based filemanager script that is easy to install and runs well on DH. I do not recommend using PHP scripts (there are many out there) for this if you anticipate needing to upload files greater than 7MB on DH, due to the limits of DH default PHP installation.
This works very nicely when set up as a sub-domain (files.yourdomain.tld, or similar), though it can also be configured to only traverse "limited" branch of a standard directory tree. You can also set it up behind apache authentication as an alternate (or additional) security mechanism.
In addition to the link I have already provided above, you might find that a little reading on all this to be helpful; here are some links to relevant DH Wiki articles:
Unix File Permissions
Unix File Permissions Cookbook