Welcome to Quilting Board and thank you for the pictures. I have a similar machine that I bought new in 1972, but is badged Alco. There is a manual, albeit not a great scan, for a Riccar that looks like our machines at
https://www.manualslib.com/manual/54...8b.html#manual I have found that if I download the pdf and open on my computer it is a little easier to read when I zoom in
I believe that you want the switch on the side to be like this to be able to sew.
You should be able to see the feed dogs raise or lower when you move that switch. Sometimes they get stuck with old oil. See if you can see the path from the switch to the feed dogs, so that you can clean and oil to loosen it up to move the way they are supposed to move. The manual doesn't say which is which, but tells about it (with different imprints) at
https://www.manualslib.com/manual/54...?page=9#manual
Are you trying to sew the stretch stitch? The stitch goes forward two stitches and then back one. That is what the dial is set for. If you just want to straight stitch, set the upper arm dial to
"0".
I have been known to set the pressure to none on a sewing machine and then wonder why when the presser foot is down that it does not advance the fabric LOL The page that the manual tells about pressure is at
https://www.manualslib.com/manual/54...?page=8#manual
I just noticed that the Riccar manual doesn't have all the stitches that yours has on the dial. If you put the dial with 0 at the 12 o'clock position the stitches in clockwise are what my manual calls Blind Stitch, Stretch Stitch (I call triple zigzag), Overlock Stitch, Overcasting Stitch, Elastic Tripple [sic] Stitch, and then the three butttonhole stitches. The numbers are for regular zigzag stitch, with 0 for straight stitch.
Hopefully, with the information that I have given, you will be able to get it sewing again.