How to configure an instance to listen on port 1433 to allow remote connection
If you are connecting from outside the domain you can either

1) Use SQL authentication to login.  If you have enabled mixed mode during the install you will have an sa account and you can create a sql login for yourself

2) There are other tricks, such as enabling named pipes and then authenticating against the IPC$ share with your domain account and then you can login using np:ipaddress in SSMS.  But beware it is a bit slow and most people don't want named pipes enabled on a production system.

But if you are connecting from outside the domain the easiest way is use SQL authentication.