Modern Orthodox is generally the Young Israel ,Orthodox Union (o-u) and Yeshiva University
The Shuls have seperate seating with Mechitza only MEN count for aliyot and davening.
They have more secular study education so many have regular jobs.
They look and dress like more like your average american except they wear kippot (No Peyot and usually not beards)
The women are SUPPOSED to cover their hair, but some do not as many who go to Modern Orthodox shuls are not as religious (You will not regually see a non-chassic person for example go to a Chassic Shtebul except for Chabad)
Because the modern orthodox shuls are more open to people than chassidic and Yeshivish shtebul and occur in not as reliogious communities many people who attend their shuls their religious observance can vary however the RABBIS are frum.