I use lantus pen..first few times its kina ctreepy...now...its like piece of cake....you just dial in the units your dr perscribed...the needles are so amall...just remember to vary your injection site...you gott this

You can use the pen until your run out of insulin

There is different sized pens and if for example it contains 300 units and you only inject 30 units the pen would contain "10" doses

Just follow the instructions that came with it to change the tip (sharp - don't ever reuse the "needle") and prep it for next use

If you google the "brand" of your pen you will likely find some video's on the product website that demonstrate "what to do"