Tresiba is rather different to most other insulin pens - I presume you have a pen? 100units/ml or 200units/ml?
I only speak for 200units/ml - a green pen.
You have to be quite careful with the dose dialling, happens quickly, and dialling back is rather notchy.
The pen is automated, you just press the button and it automatically delivers the dose you dialled.
I have used it for 8 months and am really happy. It is also a forgiving insuli.
Good luck, don't worry.