Enabling SFTP is very easy. Open /etc/ssh/sshd_config...
... and make sure you have the following line in it:
Subsystem sftp /usr/lib/openssh/sftp-server
Then add the following stanza at the end of the file (add such a stanza for each user that you want to chroot):
Match User falko
Instead of adding a stanza for each user, you can also chroot groups, e.g. as follows:
Match Group users
This would chroot all members of the users group to the /home directory.
If you chroot multiple users to the same directory, but don't want the users to browse the home directories of the other users, you can change the permissions of each home directory as follows:
chmod 700 /home/falko
Afterwards, you can log in with an SFTP client, such as FileZilla or WinSCP.