Watching the Supermoon simply means watching the Moon when it is at its closest to us.
However, this was not a supermoon, it was simply a perigee Moon.
The perigee of the Moon's orbit happens every month (once a month). The only special thing about this one is that the phase of the Full Moon happened to be at (roughly) the same time. This happens at least once a year, sometimes twice or three times.
The perigee itself (its actual distance) changes from month to month. The supermoon is the one where the Full Moon happens to match a perigee that is the closest possible over some interval. THAT is the rare one (does not happen every century -- we had one a few years ago).
The difference in appearance between a perigee Full Moon and an apogee Full Moon (apogee = furthest point away from Earth during the month) is not that much. It is measurable (for example, when doing ship navigation with a sextant, we have to apply a slightly different correction... but it is quite a small correction difference).