Entry to the Parliament building
We will enter the area at Gate XVII, which is the northernmost gate.
The entry to the building itself will be through Gate VII. These are shown in the image below.

How to get to the Parliament?
If you need to plan your way to the Parliament, I would recommend using the route planning program of BKV (the Budapest public transport company), available here:
http://213.16.82.118/tervezo/index.php?lng=eng
If you go by Metro, for instance, you can get to Gate XVII by following the purple line from the Metro sign (M) to the arrow denoting the destination on the map below.