I am a spanish speaker but I'm learning german from english. I am learning german by myself and it is a little hard. I am using http://www.memrise.com/ to learn german. The method to learn by repeat the words is good. But I want to learn the grammatical part or the correct way to make a sentence, and my question is, when I have to use ein or eine in the sentences?
In a nutshell...
Both ein and eine are articles, indefinite articles, as a and an in English, but unlike English, you have to use them with gender concordance. In German nouns might be, as in Spanish, masculine or feminine, but unlike Spanish, also neutral. Unlike Spanish, German has also an extra coordinate called case (Fall or Kasus). The case can be nominative, genitive, dative or accusative. You won't fully soon all that what case conveys, so don't worry if you don't understand all by now.
- ein as the indefinite article for nominative neutral or masculine nouns. Or as accusative indefinite article of a neutral name.
- eine is the indefinite article for feminine nouns in accusative, feminine.