It's really and truly incredibly simple.
The pen is all assembled, you just take the cap off,
The needle tips have a paper seal over the screw on bit which you remove and then you screw it onto the pen.
You take off the lid off the needle tip, often there's another cover that you just pull off.
Then you twist the knob on the end of the pen to the first little line and press it in. This is called priming the pen. You might need to do it a couple of times the first time you use the pen. You're looking for a drop of fluid on the needle tips.
Then you twist the knob and just keep on twisting for ages till you hit the number 1.
It's ready to go. Pick your spot, I use belly because it's all flab so plenty of subcutaneous fat to inject into.
Decisively but not hard just press the needle in then push the knob on the end of the pen and keep pushing till it's back to 0, it takes a bit longer than you'd expect and it's a good idea to make sure the little window with the number is facing up so you can see it before you inject. Once you hit hold it still till the count of 10 then remove it.
It is a teeny tiny super thin needle and you barely feel it. Honestly i'm not being macho or shining you on, it's almost surprisingly painless.