“Eine“ is the same as “a“ but you use it for feminine words.
In German you can also use “ein“ which is used for masculine and neuter words.
Ein Buch (DAS)
Ein Mann (DER)
So basically, “ein/eine“ is the same as the English “a“ :)
And you'll get to know other forms of “ein/eine“ when you have read something about the four cases (Nominativ, Genitiv, Dativ, Akkusativ)