In some regions of Germany it is called "Krumbeere" or "Krumbiere" as well. But this has nothing to do with crooked bears or (in German) with crooked berries, as many people think. Etymologically it is derived from "die Krume" = "the ground/the soil" and "die Birne" = " the pear".
The simple answer to this question is that "e" and "i" are definitely different vowels, so the distinction between the two words should be quite easy. The problem is that this may not help you if either (or both) of these vowels doesn't exist in your native language, as is the case for English. The German "e" corresponds to English "ee", but the German "e" doesn't have a direct correspondence. It resembles the "a" or "ai" in some respects, but it is not the same sound. In this particular case "ihr" sounds like "ear", and "er" comes rather close to "air". The best thing to train your ears is to listen to as many pairs of words as you can get hold of: "Fehl(er)"-"viel"/"fiel", "leben"/"Leben"-"lieben" and so on.
You have to learn the grammatical gender of all nouns. "ein" is for masculine and neuter ones, "eine" for feminine ones. But this holds only for nominative case. Here you need an accusative. masculine nouns would have "einen" then.
"Kartoffel" is feminine. So better learn "die Kartoffel".