Do see professionals both in vocal technique and a physician if you can afford it, since you say you've already been diagnosed with a small nodule. I have a friend who had great promise in musical theatre who had to drop out of music just after starting college due to his nodules. Nodules can be nasty business, as also evidenced by Julie Andrews' botched surgery in the late 90s, which has left her mostly unable to sing. But it seems you have found out about things early and will most likely be fine if you proceed with caution.
In the case of a vocal coach, definitely look into someone with a primary focus on classical operatic technique rather than pop or musical theater. This may or may not be your ideal choice of music to sing, but this is where all the centuries of safe and proper technique have had time to evolve. A good voice teacher trained in classical pedagogy can help you be sure you are using a safe technique.
I am not such a person, but in my experience working as a part time choir director and as a voice student, I can tell you a few brief things. (I only hope I convey them properly in print.)
First, as far as proper breathing, when you take a deep breath, you don't want your stomach to look like it's expanding nor should your shoulders be rising up as you inhale. Instead, you should feel your back expand and your ribcages spread slightly apart if you're doing it right. Think of drinking in air rather than sucking it in. A good safe sound is always one that is supported by a good breath.
More importantly for your specific case, singing without "pushing" your voice is all about achieving resonance. Much of this has to do with mouth and tongue positions that will be best explained by a voice teacher, but as a way to think of it, try talking normally and then see what you can do to project--put on a "radio announcer" voice. But very importantly, you should not feel at all like you are shouting or straining yourself. Speaking in this way, you are allowing air to resonate and build sound. Opera singers can push their way through a large orchestra and reach the back seats without a microphone or straining their voice, while pop singers can't be heard even in a small room without a microphone and while straining themselves (and their voices decline quicker over a long career). This is why. Once you've mastered doing this with speaking, apply the same to "sing-speaking" and then on to singing.
Hopefully these two suggestions will help you sing more comfortably, but I am not a medical expert nor a professional in vocal pedagogy, so I strongly urge you to consider consulting professionals (you'll also get to learn so much more!).
Take care of your voice, and very best of wishes!