Dan,
You got a decent little machine there. I did lots of fabricating with one like it, many years ago. It's a pretty straight forward machine and with the right electrodes (rods) can be fairly easy to run.
I say "Fairly", because until you get e few rods burnt up, you are going to stick a few and make a mess with some others.
As the other guys said, 6011, 6013, & 7014 and 7024 are good AC rods to start with.
6011 is a deep penetrating rod, good for slightly rusty or dirty metals. It can be used in all positions. 6011 is sometimes used for a root pass weld and then finished off with other rods.
6013 is a shallower penetraing rod that can be used on thinner metals. It can be used in all positions.
7014 is a low penetration rod that has a good flowing bead characteristic. It is to be used in the flat and horizontal positions.
7024 is very similar to 7014, but with a hotter arc. These two are used for high deposition, fast build weld beads.
The "60" & "70" is the tensile strength of the rod material. The other digits tell the positions to be used and other specifics, that I cannot remember at this time. (Sorry, but I generally consult a welding bible when I need to know that stuff. It is not available to me right at this moment) But I think I gave you something to start with.
To learn a bit about the characteristics of rods and the weld procedures you should check the:
www.lincolnelectric.com
and
www.millerwelds.com
websites. There you will find a wealth of information.
Another place to check out is
www.weldingweb.com. That group has many experienced and helpful people to help you.
Myself, I would buy a few 7014 3/32" rods and some 1/8" 6013 to practice with.
Good welding and we will want to see pictures of your results.
Aloha, Tony