Electrolux Model 6690 sewing machine user manual.

SOURCE: kenmore model 385. 12912890

Make sure your machine is set to feed material. There may be a switch or knob somewhere on your machine to lower the "feed dogs" (the little metal teeth that pull the material through the machine). If they are down, the material won't feed so the machine will sew in place. More likely, since its knotting on the bottom, your machine is probably not threaded correctly. Rethread the machine, and try again.
Yes, the thread on the bottom IS the needle thread.

SOURCE: Threading directions

http://www.sewingmanuals.com/Sewing_Machine_Manuals/Viking.htm

I have not dealt with them myself but they have all sorts of Viking manuals in PDF or CD listed. You download (or pay for a mailed CD with the PDF on it) and either view it on screen with Adobe Reader (free at Adobe.com) or best bet is to print it - suggested you print double sided duplex) if possible to keep it smaller in thickness. That way you have a hardcopy with the machine.

SOURCE: bobbin thread won't catch

I've just had this exact problem with my model 2037. The problem, according to 3 shops I've taken mine to, is that the shuttle hook (the metal piece that the bobbin sits in) is broken and needs replaced. Problem is, the piece is next to impossible to find. 

SOURCE: Dropping Feed dogs on kenmore model 19233

Pull out the removable table and you will see the drop down feed dogs switch lever behind the back of the machine. Move that lever to the left or right to have feed dogs go back to normal sewing mode OR for embroidery mode.

SOURCE: dont know how to use the sewing machine so how do i thread

well!I If you buy a new sewing machine it has a manual to guide you in any brand.But if buy a used one sometime it doesn't have a manual, you didn't mention the type of sewing machine you want to use any how if you have a mechanical sewing machine it's better to start on it.First you must know and must familiarize the significant part of machine and important usage of them,I'll just mention the most usage part at start.Putting thread in bobbins first there is bobbins winder where thread was wind,draw thread from spool through bobbins winder tension disc located at top of machine.wind thread around an empty bobbins serveral times then,place bobins onto bobbins winder shaft with thread wound on bobbins clockwise sometimes this is located at top right side a shaft coupled to circular rubber touching handwheel perpendicular sometime it was located at right side front of machine near handwheel.Release clutch by pulling handwheelor rotating pivot wheel counterclockwise at the center of handwheel whlle holding freeze the handwheel tigh in order to disingage the motion of handwheel from mechanism of machine.