Collections are free to create and are public- any Collection is searchable and discoverable by any other Declara user. Collections may show up in Google search results as well. All Insights and discussions that take place within a Collection are public as well.
Channels are essentially higher level "Collections of Collections" and can only be created when given permission by a Declara Admin. Once created, Channels are public as are all of the Collections within a Channel.
Teams are private areas that can only be viewed by members of that Team. Content added within Teams is not searchable and all Insights and discussions made within a Team are private to Team members.