EDIT2:
now in a better video format with voice:
EDIT: now in video format:
Step 1.
Open Ground Forces tab - the icon is the AT-AT walker. Then select the Unit Class Design tab.
Step 2.
Select base unit type. The options here depend on whether you're doing conventional or TN tech and how much you have researched.
Step 3.
Select the armour type. Options depend on the tech you have and what base you selected.
Step 4.
Select component type. This is the main purpose of the unit. If you're making a Medium Vehicle or heavier, note the extra component drop-down menus at the bottom!
Step 5.
Give your unit a name - this can be as simple as "Basic Soldier" or as complex as "Type-78 Main Battle Tank B-12". Then click Create and the game gives you a confirmation pop-up.
Step 6.
Go to the research window and research your unit.
I have my GC scientist Flyn Temetor already researching Geosurvey Equipment so I'm adding Type-78 Main Battle Tank B-12 to his queue.
Step 7.
Once the research is completed, you can make the ground unit formation. Go back to the Ground Forces window and select Formation Templates tab.
On the left, you see all unit classes you've created. On the left are all your formation templates.
Click New at the middle bottom to make a new formation template. Then just select the unit classes you want in your formation and click the Add Units button at the bottom. You can change the amount of units added by writing a new number next to it instead of the default 10. There is no need to save the template, it gets updated automatically.
Step 7.
Go to GU Training tab on the Economics window.
Select the formation template you want to build from the lower list. Then click Create Task. Your formation will get a default name and will be shown at the upper list.
Step 8.
once the formation template has been built, it'll show up in your Order of Battle and now you can assign a commander to it!
Enjoy!