The sender transfers files to receivers through registration of the 'share'.
Registration can be made from 'Quick Start' wizard by choosing 'Create new upload session', or from 'Management of shares' window by choosing 'Add' button.
The additional information about work with 'Quick Start' wizard is here. The information about work with 'Management of shares' window is here.
Anyway you will get to window of share registration.

Registration is passes in two steps:
- first - you prepare files list. For preparation you can user follow buttons:
Add files into share;
Add directory (with files) into share;
Remove files or directories from share. - second - you register share by pressing 'Register' button.
As a result of registration the key will be generated:

Receivers can use this key to get files. Procedure of receiving of files is described here.
See also:
Management of shares window allows you to control the list of shares.
