Hello and welcome to the forum. Thank you for this question and we are sorry you are having this distressing time! Please know that your doctor is the best source of information and it is helpful to have someone also take notes for you so that you can get an accurate account of what is said during your conversations with them. 12 mm nodules are considered quite small. Nodules are not uncommon in lungs and can happen from simple things like a past respiratory infection. Often, doctors take a wait and see approach with them and they disappear. They biopsied the nodule to determine it was malignant? Perhaps the appearance of it or if it has calcifications makes them more suspicious and they are suggesting a biopsy? Normally you must have a biopsy done to confirm diagnosis. Is this the stage you are at or have they already done the biopsy? https://www.medicalnewstoday.com/articles/317531
This nodule can be a form of early-stage cancer. If your doctor is suggesting for the operation you must go for it. As your doc can suggest you the best for your life as per his experience.
If you're still confused then you can go for the second opinion. That will be a great help, sometimes it is better to get a second opinion in case you're not sure. But I'll suggest you, go with your gut feeling.
This is a helpful patient handout providing an overview of the treatment of lung cancer: