The War on Sewing Machines

Six months ago, I bought a sewing machine at a thrift store so I could re-teach myself how to sew, since it's been literally a decade since I last used a sewing machine. Yeah, I feel old, and I'm about as clueless now as I was six months ago.

It's got to the point where I don't know if the problem is that the machines (yes, plural) I've tried to use are both old and ill maintained or if I am just that bad at using them. 

The first machine is mine. I've found a gazillion videos on how to thread this specific machine, and the only thing I can figure is that it hasn't aged well. It probably used to be white, but now it's so yellow, it's not hard to imagine its insides are gummed up with nicotine. I tried, okay?

The second machine is my stepmom's, and it's old (but newer than mine). She bought it for the same purpose I bought mine. Then she lost the instruction manual and gave up. I found it in our mudroom covered in sticky pool chemicals. I cleaned it up, and I've tried using it, but with little success. I can't find any manuals or tutorials that are specific to this machine or brand.

I'm really not sure where to go from here.