nice to hear that you are enjoying the course.
I would recommend to have a look at grammar chapter 1.4 "Talking about Gender Part 2", which explains the use of "ein" and "eine".
Here is some basic information to get you started:
In English you can say "a dog" or "the dog". When you use "the dog" then you refer to a specific dog, whereas "a dog" can be any dog. "The" is called a definite article and "a" is called a indefinite article. In German there are three definite articles "der", "die" and "das" and three indefinite articles "ein", "eine" and "ein". You use them depending on the gender of the word you use them with. For example the word for "house" in German is neuter, therefore you say "das Haus" if you are talking about a specific house or "ein Haus" if it's more general.
"Ein" is used for masculine words, "eine" for feminine words and "ein" for neuter words.
It is very hard to determine the gender of a noun just by looking at a word. (Refer to grammar chapter 1.3 for some clues) Therefore the article gives you a clue to what gender it is.
Don't worry, if you get it wrong you will still be understood.
Another thing is that the articles also change depending on the cases, so for example you might say "ein Mann" or "einem Mann" etc. (I'll stop now because I don't wan't to confuse you even more, hoever have a look at grammar chapter 6.1-6.4 for more info on cases)
I hope that helps and please ask if anything is unclear.
ein eine & einen