It seems like you've got a relatively old model here, which will unfortunately make it more difficult to find a free manual online. I think I can help you a little bit, though, if you're willing to pay for one!
How To Find Manuals For Sears Kenmore Sewing Machines
You only need to focus on the first seven digits of the model number - any model that starts with 158-1784 will have the same instruction manual.
Where Can I Find A Manual For My Sewing Machine?
I haven't been able to find any free only versions, but you can purchase a physical copy for $15 here, and you can choose to have a hard-copy delivered, or download a PDF version which you can then read from your computer or print off.