Two parted question really...

First off, I've been trying to enable my SQL Server 2008 R2 to allow remote access so my friend can view it from his RDBMS (also SQL Server 2008). I've enabled TCP/IP, I've allowed Remote Access/Connection, I've opened TCP and UDP Ports and also added the sqlserver.exe and sqlbrowser.exe as inbound and outbound rule to my firewall and I've started my SQL Browswer server so it's running (all of this is because of tutorials on google on how to enable remote access...). But for the life of me I can't get it to work. I've got the server up and running and it works absolutely fine locally so it's nothing like that...

Secondly, how do I actually test this? Could it be that it actually does work but I'm unable to test it myself and he needs to be the one who tests it? If so, how would he do it. I read somewhere about some connection string but that's doing it with code, right? Once again, I have no trouble logging on/accessing my SQL Server locally regardless of whether or not I'm doing it with code or via a RDBMS.

Hope it wasn't tl/dr; and thanks in advance

Use a different computer on the same network to connect to your SQL server either via code or SQL Management studio or just a DSN and test connection (or supply username/password and try to set a db as default for that DSN).
I've got the feeling that your friend's SQL server is on his network and you are trying to connect over the internet. If this is the case then verify that you can connect from within your own network, setup your router/firewall to forward packets received from internet for port 1433 to be forwarded to your SQL on port 1433 and give your friend your public IP (ISP assigned?).
If your IP is not static you might want to use a service like dynDNS (there are free alternatives, google for them) , so that you won't have to give your friend your public IP everytime it changes.

As a test your friend can try to use his SQL management studio to login to your SQL and if that works then go ahead and setup a linked server.

PS: Opening an SQL server to the internet if you don't know what you are doing can be dangerous for your data

Yeah I had forgot to open up/forward ports on my router..

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