One of the reasons that vinyl decals have become so popular is that they are easy to install. It does take some care to get it right but altogether it is not a complicated affair. First you need to clean the walls so that no dirt can be seen through the applied decal. Take note that the better the quality of your paint is, the less risks there are of damaging it when and if you choose to remove the decal – particularly if the decal has been staying on the wall for a few years.
Usually, the individual decals that make up you wall quote or your graphic scenery will come pre-placed on a larger sheet from which you need to remove the bottom layer to expose the adhesive before applying it on the wall. From there, you only need to remove the contour of the sheet and the individually cut decal pieces will remain sticking on the wall. If something goes wrong during this process you can always remove any of the pieces and reposition them as will seem fit.