Cleaning tension plates

There is no straight stitch plate listed in the manual. Straight stitch selections list presser foot J. You might try increasing top thread tension.

In similar project type I've used masking tape over the top of the plate with success. Start by remove and reinserting bobbin so bobbin thread is out of the way. Put a long narrow strip of masking tape over center of needle plate (front to back). Take care not to interfere with feed dogs (why narrow tape is necessary). Then rotate hand wheel... needle penetrates tape and brings bobbin thread up through tape.

wrong bobbin tension , but amazingly its actually easier to adjust the top threads tension to compensate for it , use your tension knob to slowly adjust , try an inch , slowly adjust try an inch , and so on to get a top and bottom thread tension to match , this will need to be adjusted for each major change in fabric (aka , knits to woven )

try using a small piece of tape on the thread guide and see if that
helps the thread to stop coming out of the thread guide.

Make sure the bobbin thread "clicks" into the tension slot. However, thread nests underneath are usually caused by the top thread, not the bobbin. Make sure your thread is seating itself in the top tension disks. To do this, put the spool on the machine, pull off about 12 or 15 inches of thread, then hold this thread down with one finger on your right hand as you take the thread tail through the threading path with your left hand. When you get to the needle, tug the thread (still holding it down up top) to be sure it seats in the tensions disks. You must also have the presser foot UP while you do this to ensure that the tension disks are open. Watch the first thread guide after the spool as you sew to make sure the thread is not jumping out of there (a common problem with Des1 machines, fixed with SEs - no comfort to you and me!). I have put a small piece of tape across there with the end turned back on itself so no sticky bit is going to catch on the thread.

a quilting bar attaches to one of the feet usually in the back and is attached by a little set screw. it is used as a guide to ride a long a previous line of stitching or a design to keep lines of stitches the same distance apart.
I'm familiar with 2 different types of cording feet. one looks like a zipper foot... very narrow and a notch on the side of the foot instead in the middle. to make cording ...fold a narrow piece of fabric in half and place yarn or cord along the inside of the fold.next place folded fabric with yarn inside under presser foot. but up the foot next to the yarn bump on the top side of folded fabric and stitch as close as possible. the second kind has a groove on the underside of the foot and the yarn bump follows this groove stitching is also done close to the yarn. some concideration in needle placement is needed depending on the thickness of the yarn or cord. always hand turn the needle up down the first few stitches to make sure the needle does not hit the foot.adjust if needed.