How do you thread a White Mighty Mender W100 Sewing Machine?

SOURCE: Where can I purchase a bobbin for the Mighty Mender W100 Mechanical Sewing Machine

Well, here's an easy fix. It is either a class 15 or class 66. I would go to a local repair shop with your machine and they can try either of them . They are not real expensive.

SOURCE: For the White Mighty Mender W100 sewing machine,

Same as with all machines essentially.......
Check the timing of the needle to the hook.
Here is a guide to generic principles of Timing