I am trying to build a .NET web application using SQL to query AS400 database. This is my first time encountering the AS400.
What do I have to install on my machine
You need the AS400 .Net data provider. Check here: https://www-01.ibm.com/support/docview.wss?uid=isg3T1027163
For connection string samples, check here: https://www.connectionstrings.com/as-400/
Also, check out the redbook for code examples and getting started. http://www.redbooks.ibm.com/redbooks/pdfs/sg246440.pdf