Main Routes from the South to Aberdeen will all converge at Perth then the main route North will be the A90. Sat Nav will get you to the destination. The registration hotel is the same. In the appendices you can find detailed routes from the airports that will converge with all routes North. In summary from Glasgow (Airport) you need to follow M8, M80, M9, A9 then A90. From Edinburgh (Airport) you need to follow A8, M9, M90, then A90. When you arrive you will see Aberdeen pan out across the horizon, assuming it is not foggy!
The IIC Venue has free car parking as does the IIC registration hotel. Other hotels may have supporting car parking with local authorities so it is better to check if this will be an issue for you.