Generally, this welder is only good for welding very thin mild steel. I had one similar to that about 8 years ago I picked up at a garage sale. I think the thickest I could easily weld was .125 plate. The machines duty cycle would generally kick in within about 5 minutes of welding.
I am not aware of a amuminum stick welding process, generally SMAW is designed for ferrous metals like mild steel, iron, and even stainless.
For most mild steel, you should stick with a 6011 or 6013 rod. I believe Miller has some excellent tutorials on electrode part numbers and their usage.
some electrodes are designed for overhead welding, some for any/all positions, etc. They come in different thicknesses, designed for different materials and amperages.
I think the best luck I had with my old CH stick welder was buying the rods from Wal Wart, they were 6013 rods in a 1/16" thickness. The thinner the rod, the better my machine would burn into the metal. Using the same 6013 or 6011 rod in a 1/8" diameter would barely burn into the metal.
Hope this helps a little. There should also be a guide that came with the welder that will give some guidance as to the best consumables to use.