Basic information: Aarhus has two bus networks: the city buses and the regional buses, some of which can also be used inside the city. The city buses are yellow and have two-digits numbers, whereas the regional buses are blue and have three-digits numbers. For the sake of simplicity, I will here focus only on the yellow city buses, which are also the most relevant for you.
All city buses go from the city centre to the suburbs, except 5A and 6A, who drive on the city’s two beltways. Entrance at the city buses happens through the back or middle door, exit can happen through any door. Aarhus has a self-ticketing system, i.e. passengers buy their tickets from a machine located in the middle or back of the bus. They do not show it to the driver, instead controllers ride the buses at random. As guests at the conference, the relevant ticket is the 2-zones single ticket for adults (Danish: Voksen, 2 zoner). It costs 20 DKK and is valid for 2 hours in any direction, on any number of buses within the zone limits. The machine inside the bus takes only coins. The driver might be able to help you out with change, but not always. Alternatively, the bus company has an app (https://www.midttrafik.dk/in-english/tickets-and-payment/midttrafik-app-mobile-tickets.aspx) with which you can buy multi-ride-tickets (10 rides for 140 DKK).
Upon exiting the hotel, turn left. Take the first left down Hans Hartvig Seedorffs Stræde and continue till the bus stop. From here, you can take following buses for the university (destinations are stated at the bus stops as well as on the buses): 1A towards Trige or Lystrup 14 towards Skejbyparken 18 towards Mejlby or Elev In any case, get off at the stop named Randersvej/Nordre Ringgade. When getting off the bus, cross Randersvej/Nørrebrogade. Auditorium 1 will be on your right, in the red building (building 1441, room 012).
Any building at campus can be found here: http://www.au.dk/en/about/organisation/find-au/buildingmap/
If you do not live at Scandic Hotel, you might have to take other buses from other stops. The city buses that stop at the University are 1A, 5A, 12, 13, 14 and 18. You can plan your trip using the Rejseplanen: http://www.rejseplanen.dk/ . For this, you need the address of your hotel and the address of the conference or the name of the bus stop (address: Tåsingegade 3, 8000 Aarhus C, bus stop Randersvej/Nordre Ringgade)
There will be a common dinner, which will take place at the complex known as Godsbanen (the old freight station). The address of that is Skovgaardsgade 3, 8000 Aarhus C. It can be a bit tricky to find. The closest bus is bus 12 stopping at Carl Blochs Gade/Skovgaardsgade, but since it is located 850 metres from the Park Allé/Banegårdspladsen stop (the main stop, right next to the train station and the city hall), walking is also an option. From Park Allé, walk through the City Hall Park (Rådhusparken), and then cross Frederiks Allé. Go for the Concert Hall (Musikhuset), which has a facade from glass. To the left of the Concert Hall you will find a hotel complex (Radisson Blue). Between Radisson Blue and the Concert Hall, there is a path leading downwards – the path goes along the wall of the Concert Hall. Following the path will lead you to Skovgaardsgade. Continue until you find no. 3 on your left side.
If you prefer bus, use the above mentioned rejseplanen.dk. If you walk, but are confused by the explanation, Google Maps gives you the exact same route if you tell it that you will walk.
