I decided to be a man and start doing squats

I did my first sets last night. First with nothing. Then with just the bar (standard 45lb bar), then the bar with 2 25lb weights, and finally did 3 sets/10 reps with 2 45lb weights. (I'm a weakling, don't make too much fun of me).
I feel pretty good about it. I think I had the weight a little high on my back. Theres an area near little bone on the base of my neck on my spine that's sore, but my legs feel a good burn today. I guess I need to ensure the bar is below that point. My lower back feels alright. I don't know that I'm at the weight where I should be really concerned with having a belt, but think I should definitely look into it. I'm inspired to keep it going. I felt 10 pounds of disco melt away.
I've been reading a lot of articles and threads here today, and a lot of them talk about avoiding "rounding your back". What exactly are they talking about? Bending over when going in and out of your squat? My impression of proper form at this point is to keep my back straight, but obviously at a bit of an angle. My next squat sets, I'll be looking at how far I'm keeping my feet apart and how straight my toes are pointing. Also, I was wearing some running pants, but think I need to wear shorts as my movement was maybe a bit restricted by the pants. Or I'll just go buck naked. That's not disco at all.