Hello oldlady59. I'm sorry, I don't know where the manual is packed in the kit, but maybe somebody else can remember. (I'd just dive in there, myself, and then put stuff back.)

Or, you can go to the Harbor Freight website and download the manual, and print it out, if you'd like:
Harbor Freight greenhouses

Only glitch with doing this is there are currently two slightly different versions of the 10x12 being sold through Harbor Freight. You'll see both listed on the web page above. They are still selling an older one like mine (Model 93358), and a newer one (Model 69893.) As a result, there are two slightly different manuals. There aren't major changes in the kit, but some parts have been redesigned.

I don't know if there are any model numbers on the outside of your box; if so, just click on the appropriate greenhouse model on the Harbor Freight site, and then click on User Manual to find the link for the download.

I just put up a new one back in January.. I do not remember which of the two models. One model has 4 small triangle panel pieces at the end of the gable and one model combines it with the one beside it so that it ends up being a larger panel. Mine was missing all four of the small triangle panels.. I believe they are like 18" x 12" roughly. I did not realize it until the end and I just have plastic taped over them for now. I called Harbor Freight and they said they did not make these panels anymore for that model (I guess now they just make the larger panel). I guess I would say even though it means taking everything out of the box, it is worth it to make sure all the panels are there. The only other tips I would offer..
1. Order the extra panel clips
2. Plan out your bracing and shelving so that you insert all the T-Bolts (I grinded down carriage bolts) so that you get them all inserted and inserted in the correct order. It is a pain to have to go back and undo the roof to try and get them all in.
3. I used the U Shaped Channel for the end braces instead of the angle pieces.. it seems to give it more support.
4. I also used the 3 electrical conduits across the top... I think I am going to go back and add two more, not because I need the extra support, but because they are nice to have for hanging baskets and for trellis.
5. Go ahead and plan on getting a fan and thermostat. I do not know what to tell you about the vent openers. I am not using them currently but I do need to add some very soon to work in conjunction with the fan. The vent windows are really the only thing I was disappointed in on the greenhouse.

I am loving the greenhouse by the way.. I know you will too.

Trigolfer, thank you for the heads up about Harbor Freight discontinuing the small triangular gable polycarbonate panels for the back wall. My greenhouse is that style also, and I need to replace all those panels...and I had wondered. I'll just have to order the new style back panels and plan on cutting them to fit my older frame.

I hope you can find a solution for your missing panel pieces. If they are sending you other panels, you'll find the polycarbonate is super easy to cut with a mat knife and straightedge.

I agree that the electrical conduits are handy; I have not hung plants from mine, but ran the power cords to my thermostats along them, so I could hang my thermostat box roughly in the center of the greenhouse.

We are also on the same wavelength regarding the vent windows too...my least favorite part of the HF kit.