The Midheaven (MC) is the sign that was highest in the sky at the time of birth, and so is dependent on the time of birth and longitude. Someone born in London, UK will have the same MC as somebody born at exactly the same moment elsewhere on the same line of longitude.
The Midheaven is the tenth house, and can be placed in the chart by referring back to the table of houses and looking down from the column marked "10" to the relevant Sidereal Time and noting the sign and degree. The MC is the point in the chart that most accurately represents our aspirations and goals, especially in our career or working life.
The opposite point to the MC is called the Nadir (IC) and this can be placed in the chart if desired.
At this point the section of the chart marked "Qualities" can be filled in by counting the number of planets placed in the polarities, elements, and quadruplicities and noting the ruling planet (the planet which rules the sign on the Ascendant), ruler's house and any rising or angular planets.