The typical way of getting from the hostel to the conference venue is: walk along Mazā Lubānas iela (street) and Rēznas iela to Valerijas Seiles iela. There you will find a bus/trolleybus stop ('Rēznas iela'). Take a trolleybus No. 15 towards the city center. Leave the trolleybus at the stop ‘Centrālā stacija’ (Central station; the 7th stop). At the same stop, take the bus No 22. and leave it at the 3rd stop ('Nacionālā bibliotēka' (the National Library)). Walk to the conference venue as shown in the map here.
To get from the conference venue to the hostel Prima, the most convenient way is to take the bus No. 23 at the bus stop across the street in front of the conference venue (these are rare, however). Get off it after 4 stops ('Centrāltirgus'). From that stop, take the trolleybus No 15 going to Ķengarags direction. Leave the trolleybus No. 15 on the stop ‘Rēznas iela’. Then walk alon Rēznas iela and Mazā Lubānas iela to hostel Prima. Ask Google maps for the directions if needed.
If you do not want to wait for the bus 23, walk to the National Libaray bus stop and take bus No. 22 or 25 going to the center direction (across the bridge) and leave it on the stop ‘Centrāltirgus’ (the 3rd stop). At the same stop you will get the trolleybus no 15.
Please consult the bus and trolleybus timetables.