What you have is some scrap hot rolled mild steel. It appears at some time, it had been painted reddish.
The welder you bought appears to be an Amazon prime day clearance of some kind. YesWelder's web site does not show this as a model? In general YesWelder's stuff gets mixed reviews. Many newbie posts happy to have gotten the welder, several disappointed experienced welders. I'm guessing you paid close to $100 for this thing? If it works once...
Users complain that YesWelder will not provide service to anyone who bought their welder off Amazon. I'm guessing this means some entrepreneur bought out a lot of substandard welders and blew them out on Prime Day?
The usual rule that a man that buys cheap tools may apply here. You'd have been better off buying a Harbor Fright Titanium stick welder, at least there are reviews that show they work.
Now on to your project:
Pretty much the most common rod to use on mild steel is 6013. I'd suggest you start by practicing on some scrap. Be sure you clean the paint off b4 you weld. The steel you have looks a bit light, is it 10ga? Try welding at 100amps then. Be sure to brace the frame on the diagonals as the thin stock will flex too much otherwise.
Post photos of the result!
Astrobuf
