You must thread the "Loopers" (the metal arms inside) before the needles. If you do it out of order, the threads will tangle and snap immediately.
If the loops are hanging off the edge of the fabric, tighten the looper tension. If the fabric is puckering, loosen the needle tension.
Turn it up to prevent the fabric from becoming "wavy."
Watch the Singer S0105 Instruction Video for a complete walkthrough.
Explain how to fix (like skipped stitches).
The in your query likely refers to a video file format. Many users search for "S0105 3GP" to find quick, mobile-friendly tutorial videos to help them thread this specific machine, which is notoriously the most challenging part of using one. 🧵 The Story of Your S0105
The S0105 features a differential feed dial. This controls two sets of "teeth" under the needle.