Hi and welcome to the wonderful world of modding ATG
I assume you already found the SFT menu, where you define the various abilities of a Subformation? If not it is the RED outlined square in the picture below, that is a snippet from the top left corner of the Editor. If you have done that, click the one I have outlined in YELLOW. That is the Item menu. Here you make Items, that is everything that can be produced.

- Making SFTs 01.jpg (41.05 KiB) Viewed 462 times
Once there, click on the button with a plus in it. I have outlined it in the picture below, again, in RED.

- Making SFTs 02.jpg (16.04 KiB) Viewed 462 times
Once you have clicked that, a "Default Item Type" will be made, at the end of the list of items. You rename it by clicking on the Button I have outlined in the GREENISH color. You Can make a regime be able to produce it by Selecting the regime number(s) (or maybe it is people number(s)) in the box outlined in RED. Once you click on it, you can set it to True or False.

- Making SFTs 03.jpg (112.2 KiB) Viewed 462 times
Don't forget to select the ItemType Group, in the PURPLE box. It is the one that determines under which heading in a city the Item will be produced.
And finally the YELLOW box is where you set the cost of it, in Production points.
Now all of this doesn't work of course unless the item is connected to the SFT. You do this by selecting the IsSFTType# button, 4th from the bottom. (Ran out of colors, and forgot to outline it too).
Now you may ask why have this submenu. Well, with it, you are now able to make several different costing items that produce the same SFT. So in other words, if you want Germans to produce Tanks cheaper than say the British, then you can do so, without making a new SFT for it.