The sill guards come with an adhesive backing, protected by a tear-off paper-strip. The instructions say use an alcohol wipe on the sill first to clean it. Then mark with a pencil 6mm from the edge of the sill. Another pencil mark locates where the end of the guard is to be placed. Then carefully place the guard on the sill, pressing down hard for 30 secs. The adhesive should be allowed to 'harden' for 24 hours before the guard is trodden on. Easy!