If you open the front face plate, you will probably find a threading chart.
I have a Singer Golden touch and Sew, Model 750 that I bought new circa 1970. About 5 years ago, I had to have all the plastic parts inside replaced. Plastic does a funny thing when it "rots". It starts coming apart and if there are cogs involved, the ends just start coming off. Since a 774 should be a newer machine than my 750, maybe you don't have any of this type wear. And, yes, my machine was well used for many years. So, threading it properly may not solve all your problems. I could sew a straight seam when mine started coming apart, but it wouldn't zigzag. It has the most beautiful balanced stitch of the 4 machines that I own, although I tend to use my Big Brother because of the thread cutter and auto threading function.
Edited to add: Found your manual
http://www.singerco.com/uploads/down...84_774-734.pdf
I downloaded a pdf for mine as well. I still have my original manual but decided a virtual one would be good.