How to glue wallpaper

The wallpaper of the walls with wallpaper is considered the simplest stage of repair, it seems that no special skills are needed: I cut off the canvas, smeared it with glue and put it to the wall. Well, if there is a drawing, you still need to combine, which, however, is also not particularly difficult. And then it turns out that here the corner is moving away, but there were some bubbles there… In general, it is better or to entrust the case to professionals or to carefully study the technology in advance.