ぽい is simply another term for みたい when you are speaking of a resemblance.
My that sounds awfully professor-ish don't it. Ahh, much better.
If you haven't yet learned ～みたい, then I suppose I should be the lucky one to teach you!
Example: その赤ちゃんの顔がりんごみたい。 Sono akachan no kao ga ringo mitai. That baby's face looks like an apple.
You may never have any reason to use my example sentence, and I'm sorry that I can't be useful all the time =(
Now to sound a little more native, you would simple substitute ぽい for みたい。
その赤ちゃんの顔がりんごぽい。 Like that!
And you're a step closer to using the Japanese that Japanese people use!