The square foot is a unit of area and is an imperial unit with the symbol ft².
One square foot is equal in area to a square with edges one foot in length.
It is used a lot in expressing the internal size of a house, apartment, office or other properties so is a useful unit to understand.
The hectare is a unit of area and is a non-SI but metric unit with the symbol ha.
It represents the area equal to that of a square with edges 100m long (ie 1hm² or 10,000m²). This is the equivalent to about 2.47 acres.
Its size is down to its use primary use; that for measuring the size of land.