When you're preparing the canvas for a detailed portrait in oils or acrylics, you want the surface to be smoother than a regular canvas texture. This video shows you simply and clearly how to go about it.
Note that the artist (via the translator) refers to his preference for Linen canvas, because of its strength and quality.
The video also shows you the correct way to insert those wedges in the slots in the back of the frame to square it off and ensure you start with it stretched properly.
I hope you found this tutorial useful. It shows that you can't always just pick up a canvas and start slapping paint on it! Sometimes, a little preparation can make a big, big difference.