These days, most wallpaper is pre-pasted, and is much easier to handle. To prepare the wallpaper and release the glue, fill a water trough (available at home improvement stores) full of lukewarm water.
Take the strip that you have cut and roll the strip loosely, starting with the patterned side on the inside of the roll (the glue side facing out). Place the roll in the trough and soak for one minute, or according to the instructions on the wallpaper packaging.
Hold one edge of the strip with both hands, and lift the wallpaper from the water. Your partner can help by keeping the wallpaper straight as you lift it out of the water. Check to make sure that all areas of the strip are sufficiently wet.
To glue un-pasted wallpaper, lay the strip on a large flat surface, with the pattern side down. Use a paint roller to apply wallpaper paste to the strip. Be sure to wipe off your work surface before you lay the next strip down.
After preparing and pasting the strip, you should fold the wallpaper using a technique called “booking”. (Be sure to read the instructions on the wallpaper packaging, however, because some wallpapers should not be booked!) To book the wallpaper, start with the pasted side up and then fold both ends of the strip to the center. Do not crease the folds but let them lay loosely.
For pre-pasted wallpapers, you should let the book sit for about ten minutes, so the glue can “cure”, unless the directions on the packaging indicate otherwise. If you are covering a ceiling or hanging a wallpaper border, you should very loosely fold the glued paper into an “accordion” book.
This means that you should fold the strip back and forth with the pasted side up (like folding a fan out of paper). This makes long strips easier to handle. Again, let the strip cure for about ten minutes, unless otherwise directed.