Menewsha Avatar Community - What is (excluding tone) passive sentence structure?Confused

Okay, I was told by my history teacher in a report that she took points off because some of my sentences were passive, not the tone of the sentences, but just...the sentences. My tone was actually spot-on opinionated. It was a paper about point of view. But, anyway, she told me my compound sentences were passive. And then she told me that everything else about it was great, but that I'm not going to learn anything new if that's all I hear. Sure, I agree with that, but she could have at least explained it a bit.

I asked my English teacher how compound sentences could be passive. She gave me this look and said, "Actually, your writing style with your sentence structure is passive. A lot of kids think it sounds better, but it's not." And she's always telling me how great I write. And a lot of people think I write really well! So I'm just like, sad that I don't get something about writing. It's my strongpoint. So I'm just kind of like, "D:..." confused. And I asked her what makes a sentence passive. She said that a passive sentence has a verb acting on the noun, and that better sentences have the nouns actually doing something [or something like that]. I think I got it for about two seconds, but then I lost it. The bell rang, telling me I should sit down, so I just sat down and pondered to myself what the crap she just said.

So, can somebody in the literature/writer's forum please tell me how I can make my writing sound better than it already is?