I did not know what to expect when I installed the software. It first asks you to create a profile, this indicates to the program (after you have it all set up) which folders are being shared and which peers can connect to you. Each profile can have different settings and shares and will have a separate encryption key. It then asks you to create an encryption key passphrase, this helps you access the key when signing in and adding peers.
Once the program is installed you will see a sidebar and some tabs at the top. Some of the icons on the sidebar are shortcuts for functionality buried in the menus at the top. You can add friends by clicking on the add icon and then choosing which method you want to add them with. You will send them your key if you want them to be able to access files on your computer, and they will send you theirs if you want to access files on their computer. Chat functions work once at least one person has shared their key between the two of you. Friends can be assigned to groups and details can be entered like can be done with email.
Sharing files is rather straightforward, appearing as a normal P2P transfer, if you are familiar with sort of thing. Multiple locations can be shared, the location shares are not encrypted however, merely the connection between peers. Once you have a share setup, your peers can browse your share location and download whichever files they choose. You can regulate the number of up and down shares, bandwidth, and other details in the settings panel.
There is also a message function, separate from the chat feature that functions very much like email in that you can send it to multiple users and it is private to those users, unlike chat.
Retroshare is a valuable little tool, especially for small businesses and home users that need to share file to peers and that require a secure connection and secure communications. I could imagine this tool being especially useful for employees of a small company who telecommute and do not have a VPN available, perhaps because the company has no network, or perhaps even no office.