Because you installed x64 - all you really need to do is set the max memory for SQL Server. Since you installed the standard edition, you probably should not set it any higher than 12GB as there are issues when you allocate more.

There is going to be a post SP3 hotfix available soon that will allow Standard Edition the ability to lock pages in memory. When you have that - then you could increase memory above 12GB to 14GB and grant the lock pages in memory right to the account running SQL Server.

On x64 - if you don't set the max memory SQL Server will consume all memory on the server and starve the OS (eventually, unless your system never needs all of the memory).