welding 101

I'd turn the voltage up a little if not a voltage tap machine. Some of the welds look "wormy".

Generally,
Popping wire is too much wire, not enough voltage
Hissing and wire burn back towards tip is too much voltage, not enough wire.
Find a point in the middle.

If you hear any popping, likes sometimes bacon makes when cooking, turn up voltage or less wire. You want a hard sizzle, no pop, like in the miller video. You will likely pick up your travel speed a bit as well.

Clean, clean, clean material. Shiny after prep with a zirc wheel and wiped down with acetone is my method.

Make sure your machine is set up properly. When I got my Miller, I set the feed assembly up too tight, squishing the wire to a diamond shape. Too much drag on the spool holder, too much pressure on the feed. Made a mess of things.

It helps if someone skilled can come by or go get a quick refresher course/help. One of the members had me at his shop and helped me a bunch with technique and set up. Showed me some neat techniques to reduce sunburn! Makes a world of difference and stopped some floundering.

Practice and be patient.