You can listen to the lungs, including the bases of the lungs, from the anterior side. I don't do it like that. If I'm doing a quick evaluation of the lungs, I will listen to the top of the lungs from the anterior side, and then the bases from the lateral sides. If I need to get more specific, then I will listen to the anterior, lateral, and posterior sides. Review the lung anatomy and you should be able to figure out where you would need to listen to the lungs.
You should also be able to find multiple references on how to listen to lungs on YouTube or other websites. The stuff is not exactly hard, but it does take some practice to get good at it.
Something to remember is that you need to do your assessments the way you were taught to do, not the way that you see it done, because the nurses that you are observing do it their way, and have their own licenses on the line. You, however, do not have a license on the line in the same way that they do. If you do not do your assessments correctly, as you were taught to do, you could fail clinicals, and that would put you way back in terms of getting a license of your own.