yes. it is always used in oral Chinese. and i think Sherry answered well. i want to add another point that 把 is used in a passive response. For example, i ask you 我放在桌上的苹果去哪了（where is the apple i put on the table?）then you can ues 把 to reply me: 我把苹果吃了. The difference between 我把苹果吃了 and 我吃了苹果 is the situation, the former is a passive answer, of course, the latter is a positive expression, a statement. for example, i ask you 你晚餐吃了什么？（what did you have for your dinner）you can respond to me in this way, "我吃了苹果" i ate apple for my dinner. That's it. Hope it is useful to you.

The rules for using 把, when and where to use it and not to use it, are a bit of a grind. I have a two page section in my book I can send you if you want a thorough understanding of it. Alternatively, download the text here: http://www.archive.org/download/FSI-StandardChinese-StudentTexts/FSI-StandardChinese-Module06MTG-StudentText.pdf Go to unit 5, reference notes on page 214. It's all there.

yes. ”把“is commonly used in the speech of our daily life. In fact, we use “我把苹果吃了”more often than that " 我吃了苹果", although both of the two sentences are right, the former one is more nature and understandable . Hope to help you !

Yes. "把" is used very common, especially in oral Chinese. Both of the statements are correct, but I think there is a little bit difference. 我把苹果吃了，the point of this sentence is that the APPLE was eaten by me. 我吃了苹果，the point is that I have eaten something.

yes,"把" is very commonly used in short speech,it can mean an order,for example:把这个杯子放在桌子上 it can also mean a statement,like:我把苹果吃了