It also means that if you delete a file from one collection, it is deleted from all collections!
To add a collection, in the area Managing, Instruments, Reporting select an existing collection (or My collections as the root), and click Add --> Collection. Then enter the new collection name in the form:
The new is added as a sub-collection to the collection you first selected.
With the help of the context menu you can rename or remove a collection. To do that, hover you mouse over a collection name, then click a small triangle appearing next to it and select the necessary action. You can also move it to another level by clicking Organize and then selecting the higher-level collection in the form shown below:
If you delete a collection, the files belonging to it are safe, they are automatically moved to the My collections root level.