When you upload a unit to Clilstore you agree to release it under one of the Creative Commons licences. The default is the Attribution-ShareAlike licence whereby other people are free to copy the unit, alter it, and even make commercial use of it, provided that (1) they acknowledge your work (a link to your Clilstore unit is sufficient), and (2) if they alter it or build on it they may only distribute the resulting work under the same Attribution-Sharealike licence. However, when you create the unit you can choose instead to publish it under one of the other Creative Commons licenses, perhaps specifying no commercial use for example, or no alteration of the unit - although people would still be free to copy it.
By uploading the material, you are declaring that the work is your own, or that you have permission to release it in this way - in which case you should give the original author credit.
This applies only to material actually stored in Clilstore. If your unit links to videos or soundfiles stored elsewhere, on Youtube or Vimeo or TED for example, then these will be covered by the conditions of these other sites. But of course, if you link to material which you know infringes copyright, then you are also guilty.