You can get regular, direct trains to Shrewsbury from various places around the country. The railway station in Shrewsbury is approximately 20 minutes walk away from Shirehall. If you prefer, you can take a taxi from the station there is a taxi rank at the train station.
The bus station is a three minute walk from the train station:
Walk to the very top corner of the train station car park (the traffic lights should be on your right)
Cross the road and walk down the pavement (on the left side of the road) in front of you
You will come to a set of traffic lights and you will see the bus station