to put a secondary in the same data center, you have to create a second server. That server is the connection string you would use. Putting a secondary in other data centers, again, you're creating new servers. Connecting to the database is through those other servers.
"The credit belongs to the man who is actually in the arena, whose face is marred by dust and sweat and blood"
- Theodore Roosevelt
Author of:
SQL Server Execution Plans
SQL Server Query Performance Tuning