To stop you having trouble with paper 'falling of the wall' then you need to prepare it properly. Walls must be dust free, mildrew and grime free, (clean with sugar soap or bleach). Walls need to be cleaned, primed and sized before hanging paper.
In most case , wallpaper adheres more easily if a primer-sealer is applied to the wall. This compound keeps the wall surface from absorbing moisture from the adhesive and also protects the wall from damage if the covering is later removed. Walls painted with a high-quality flat alkyd paint may not need a primer. Choose a primer-sealer designed as a wallcovering undercoat. Apply it with a roller at least 24 hours before hanging the wallcovering to allow it to dry thoroughly. When hanging a light coloured paper over existing wallpaper or a coloured wall, use pigmented primer-sealer matched to the paper's background.
No, this has nothing to do with measurement. A liquid coating designed to make wallpaper apply and adhere better and go on more easily. It helps the drying process (so the glue doesnt simply soak into the wall) increases slipage so manovouring the paper is easier and finally adds a barrier so the paper can be removed later on.
Most modern day papers are pre-pasted so paste is not usually required. For some heavy vinyls and murals you do need to "paste the wall" or the back of the paper. Read the papers instructions or symbols to work out if you are required to buy paste.