In its simplest form:
CREATE PROC dbo.createnewdb (@dbname SYSNAME)
DECLARE @sql NVARCHAR(MAX) = N'CREATE DATABASE ' + QUOTENAME(@dbname);
EXEC dbo.createnewdb N'newdb';
There are too many considerations to list here before creating a stored procedure like this and allowing folks to call it but something like I showed should get you started.
__________________________________________________________________________________________________There are no special teachers of virtue, because virtue is taught by the whole community. --Plato