You cannot chroot* an FTP or shell user yourself. Regular FTP will be chroot'd to the user home directory and Secure FTP will not be chroot'd.
For web access, you can use the Re-map Subdir panel to map a URL path to a directory, so that
http://domain/uploads/ maps to /home/username/uploads/ for example. This would work well for the situation where the person downloading the file does not need FTP access.
If one uses the shell, they can copy the files from one home directory to another if the permissions are set appropiately. This would work well if people are sharing management of the files.
* "chroot" means to confine access to the filesystem to a particular part of the directory tree. Attempts to access any other part will fail.
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