How i descompact the course?

[DanielGoldeneye]

I downloaded a course and it is in the format ".collection", how i descompact and access it?

[SectorVector]

Can you provide a link to the download ?

A simple web search for '.collection file extension' gives you this.
"File collection created by Adobe Bridge, a file organizer for the Adobe Creative Suite; contains multiple virtual files that are actually references to files located in different places on the hard drive; often used for organizing images without moving them." Source