Ana, I have had a quick look at the video and the basic idea is that Selkirk wanted to buy land along the Red River which is now known as Winnipeg. He started in 1812 but realised that he needed title (proof of ownership) to the land. According to the British Government the land belonged to the Hudson Bay Company who had been given title to the land by Royal Charter (Order of the King) about 150 years earlier.
He bought a 116,000 square mile plot of land for 10 shillings as the Hudson Bay Company wanted the land settled. In 1817 Selkirk went to Red River and realised that he should get a title document from the 1st Native People (the local indigenous population). He had a treaty drawn up which was signed by 5 local 1st Native People leaders (signed in the form of the animals which represented the people). This treaty agreed that the settlers could stay.
This is only a brief summary of the main points.
Hope it helps