Fullscreen

As to play the game in full screen? I'm designing the game for mobile devices, and I would like to display in full screen. How should I do it?

Project properties - full screen in browser - choose your favourite setting

I select an option, but the sides are black, is not in full screen, is the most suitable option out there. How I can remove those black side?

Using scale inner will remove the black sides, but it could also make your layout area too small.

This tutorial helps when trying to make your game look good on devices with different screensizes.

Multiple screensizes tutorial

I guess that you tried the "letterbox scale"

This has to do with the dimensions/ratio of your project. Construct won't stretch a square project (let's say 512,512) in to a wide screen rectangular shape like 1280,720 (16:9).

It will stretch and fill the height (512px -> 720px) and it will leave 256 pixels of black borders to the left and right of the project (1280-768=512/2=256), in order to keep the square proportions.

If you try "scale outer", construct will fill the black areas with content from your layout, some times though this isn't desirable because it messes up with the framing of your project, and by framing I mean what things you allow the user to see or not with the window dimensions.