In your example you could use a formula to create your result; something like (Year * 100) + Month. This will give the calculation 201100 + 8 = 201108.
However this is only possible because you know the format and length of the data being input.
If you want to ‘join’ numbers where you don’t know the format then you could check one of the example forms in the help documentation. This is one of several useful examples that are worth checking out when you get a chance.
You can try the example out and will also be able to download a copy of the form to see the behavior used.