the 6 constant mitzvot
Mitzvos are generally classified into two categories, time-bound and not time-bound. Time-bound mitzvos can only be fulfilled at certain times, such as eating matzah on Pesach or waving the lulav on Sukkot*. Even most mitzvos that are not time-bound cannot be fulfilled all the time. For example, one cannot fulfill the mitzvah of mezuzah if one doesn’t have a door.
There are, however, six mitzvos that Jews are instructed to fulfill at all times and in all places.
*The numbers indicate the order and direction to wave the lulav in the sukkah.
edited from Rabbi Jack Abramowitz
…for more information on Sukkot see the Jewish Holidays.