We get the gist that somehow the people Jesus is talking about are less than upright in their actions. The details elude us, for this is unfamiliar activity. This scripture is referring to the phylacteries worn during morning prayers.
Phylacteries is the Greek name, tefillin is the Hebrew, for leather boxes bound by a leather strap.
The parchments are hand lettered and may be executed only by an approved scribe. The shel yad is placed on the left inside arm so as to allow the box to rest against the heart when the arms are folded. The shel rosh is worn on the forehead, between the eyes to rest on the cerebrum. When worn, they are for both morning and evening prayers. The other aspect mentioned above is the tassels of the prayer shawl.