The first thing that you need to do is to lightly mark the walls using a measuring tape to get a better idea of how to position the wallpaper panel. Use a level to mark the registration lines at the height of each paper as well.
Once you are done marking the walls, turn your attention to the powdered glue that came along with the wallpaper panels. Gradually, add a small amount of powder to water while stirring until the glue reaches a water consistency. If you notice lumps, keep stirring until they disappear. Leave the glue alone after that for a few minutes.
Now that you have prepared the glue, start painting it onto the back of the wallpaper panel. Make the strokes long and even, while ensuring that you cover the entire back surface.
Wait for a minute after applying the glue on the back of the panel before bringing it to the wall and lining it up with the level registration line that you marked using a level in the first step. Be sure to use plenty of glue on the panel so that it does not start peeling from the sides.
Once you have lined up the wallpaper panel to the wall, smoothen it out using a wallpaper brush. Be sure to take care of all the big bubbles and bumps.
Flatten the panel even further using a wallpaper roller. You may notice some glue on the sides of the panel. Wipe it clean using a damp cloth or sponge. Be very careful while wiping the excess glue, as you may end up ruining the wallpaper by being careless.
After you are done putting the first wallpaper panel on the wall and wiping off the excess glue, move on to the next panel until all your wall is covered.