Here is a technique quite easy to implement and robust to install plastic wall corners that does not require glue, nails or screws.
The advantage of the plastic corner versus the metallic corner is that it is easier to cut (a scissor is enough) and they can adapt quite nicely to corner. However, if you use screws or nails to attach a plastic corner to the wall, it will deform and that might give bumps and an uneven surfaces. Typically, that type of corners are glued to the sheetrock.
However, I found that approach to be unreliable. The glue would be absorbed by the dry sheetrock and the corner would not stick to the wall. Even if it manages to stick to the wall, any pressure on the corner to apply the joint with a knife would move things. It can be quite frustrating: believe me I tried it!!
Here is a solution: tape the corner to the sheet rock using painting tape. I use a cheap tape like that one below: