Assuming I have only the class name of a generic as a string in the form of \"MyCustomGenericCollection(of MyCustomObjectClass)\" and don\'t know the assembly it comes from,
Once you parse it up, use Type.GetType(string) to get a reference to the types involved, then use Type.MakeGenericType(Type[]) to construct the specific generic type you need. Then, use Type.GetConstructor(Type[]) to get a reference to a constructor for the specific generic type, and finally call ConstructorInfo.Invoke to get an instance of the object.
Type t1 = Type.GetType("MyCustomGenericCollection");
Type t2 = Type.GetType("MyCustomObjectClass");
Type t3 = t1.MakeGenericType(new Type[] { t2 });
ConstructorInfo ci = t3.GetConstructor(Type.EmptyTypes);
object obj = ci.Invoke(null);