This may be of help: How to Thread Necchi Sewing Machine
Even though your machine is probably a different model, machines generally thread the same.
Something that may help is ALWAYS RAISE the presser foot when threading the top thread. This allows the thread to seat fully in the tension disk and helps eliminate those loose threads under the fabric.
If the bobbin thread still just lays on the fabric, the top tension is too loose. Tighten the top thread tension so it will pull the bobbin thread up into the fabric. Tension is a tug-of-war between the top and bobbin threads. Neither should win nor lose. Tension is accurate when both threads meet in the middle of the fabric. Also, keep in mind that tension is not static, ie it will most likely need to be adjusted whenever you begin a new project because the thread, fabric, needle, and stitch selection can change the tension.
You shouldn't need a separate spool for the top thread if your machine has the vertical spool pin. Most spools will work unless you are trying to use the huge spools that are made for sergers. In that case, you can wind thread onto a bobbin and then use the loaded bobbin as your top thread--in effect, you would wind 2 bobbins, one for the bobbin thread and one for the top thread. If my thread spools are taller than the spool pin (causing the spool to flop around when I stitch), I simply slip a plastic drink straw over the spool pin and, Voila!, the spool pin is taller than the thread spool.
Another helpful hint: AVOID using old or bargain bin threads. Quality thread will limit a lot of sewing problems and frustration.
Install a brand new needle every 8 hours of sewing time. Frequently, problems are a result of using old, damaged, or dull needles. When having problems, the first course of action is replace the needle. A lot of time can be spent trying to find resolutions to a problem when a brand new needle is all that's needed. If you hear the needle strike something strange, it's probably best to replace the needle as it has probably been damaged or bent. A hard strike of the needle can knock the machine out of time which would require a visit to the service repairman.
Second step to problem resolution--rethread the machine. Remove the thread completely from the machine and start over from the beginning. Verify the thread path is correct.
Also, using the correct needle type and size for the project is important. Don't use needles whose eyes are either too small or too large for the thread. Use a needle made for the type of fabric and project. Use embroidery needles when embroidering, use ball point needles for knits, use sharps (universal, microtex...) for woven fabrics, leather needles for leather, denim needles for denim/heavy fabric, etc.
Last but NOT least, perform maintenance on your machine every 8 hours. Clean lint and loose threads from the bobbin area, the feed dogs, and under the needle plate. OIL (use good quality sewing machine oil) and apply just a drop or two every place according to the manual. Do NOT use 3-in-1 oil, cooking oil, motor oil, WD40 or any oil other than fresh, good quality sewing machine oil!