If you have a Knowledge Organiser buddy to share ideas with you can send personal messages. Just use the "My Messages" item on the left hand main menu. These messages are private and no-one can see them other than the sender and the recipient
If you are an Uploader Member you can attach files to these messages. So for example, if you are creating a new Knowledge Organiser and it is in draft format, you could send a copy to another member and ask for their opinion. Attaching files is only available to Uploader Members. Ordinary members will not be able to attach files, but they can receive files from Uploader Members.