I currently have a stored procedure in which I want to insert new rows into a table.
insert into cars
(id, Make, Model)
v
With SQL Server you can use the function NEWID. You're using C# so I assume that you're using SQL Server. I'm sure other database system have similar functions.
select NEWID()
If you're using Oracle then you can use the SYS_GUID() function. Check out the answer to this question: Generate a GUID in Oracle