Search on Google for the manual

Use manufacturer's name - Coronado
and the model number - whatever it is
and the words - User manual
and then try "threading diagram"

It's probably out there somewhere.

The top thread tension is usually very straight forward, and most likely is very similar to a lot of other brands. If you can't find the manual for your particular machine, a model very close to it usually does the job. These machines are often described as "badged machines" and "model 15 clones". You can probably find an identical machine to yours with a different name and "badge", user manual will also be the same. They are often very nice machines, dependable and nice to work with. Yours looks like it's in good condition, and they are usually worth spending a bit of time and money on if needed. These are very dependable work horses, simple straight stitchers not made to day. The advantage is they are usually solidly built, and yours looks like it might be old enought to have all metal gears, that's top notch in a vintage machine ;- )

Oil it regularly and frequenty, lift all lids and plates, you might have to unscrew a couple of screws. The under side needs attention too, there's a few places needing oil there too. All moving parts needs oil, where metal touches metal, gears, hinged parts, etc. Triflow is superb, but any good sewing machine oil does the job. A bit of cleaning might be necessary, it's surprising how much lint, thread and dust can gather in the bobbin and feed dog area. When you don't have the manual, your intuition is the best guide. With a bit of time and effort you will most likely find a useful manaual though.

It's a bit hard to see from your picture, but I guess the tension mechanism is on the side, where the side plate is. That's a mark of a model 15 clone, along with the class 15 bobbin case. Any Singer model 15 thread guide, or any model 15 clone guide should be helpful. Place the spool of thread on the pin on top, look for thread guides along the way; the route is towardsthe tension mechanism with the dial on the side (usually the thread goes inbetween two disks there), then to the moving arm. This is the tricky area, it might be very simple, or the might be some looping around the tensioner and the thread guides there. These newer machines often thread a bit more simple and straight forward than the original Singer 15 model.

then towards the needle bar. Look for the last thread guide on the needle bar, it tells you which way to thread the needle. It's either from the right to the left; left to the right or front to back. Needle threads from the side this last thread guide is placed to the oposite side. It tells you which way the needle is put in too; the needle threads from round side of the shaft to the flat side. The flat side faces towards the oposite side of the thread guide on the needle bar.

When test sewing use a general sew it all thread, not too thick like top stitch or extra strength. Sew two layers of light cotton fabric, quilting type, or shirt type weight. If the dial is numbered from 0-9 start with a setting between 4 and 5.

I found a picture with a threaded machine same as yours!

http://4.bp.blogspot.com/-w1EDdX1uAMU/Tp9pkiy8nuI/AAAAAAAAAFU/uCKiq-cyAR4/s1600/Picture+011.jpg

It's taken from a very nice blog, with interesting info :- )

http://mivintagesewingmachines.blogspot.no/2011/10/coronado.html

Thank you so much for the information. You have given me more information in your post than I have been able to find searching for two days. The picture you posted is identical to mine, you are correct. I was able to sew with it but something just wasn't right because the thread was not catching on the little spring. Now I see why. Yes, the machine was given to me and is in excellent condition and very clean. I couldn't believe she wanted to give it away. I think she was going to pitch it. I love these old machines because they are built so well. This is my fourth old machine that has been given to me, but this one so far I like the best. She purrs like a kitten. I travel around a lot with my husband due to his work, so plan on taking it along to use for sewing quilt blocks, etc. The box cover makes it easy to tote around. Thank you so very much for the information.