They (the men) have a tomato=Αυτοί έχουν μια τομάτα. They (the women) have a tomato=Αυτές έχουν μια τομάτα.
In this sentece αυτοί and τομάτα are not related in any way grammatically.
Can someone please try and explain to me the difference between μια and ενα? In what context should either be applied? I'm so confused by something that is probably quite simple. Βοήθεια!
Ένα applies to neuter nouns, whereas μία is the feminie form of the indefinite article. So μία γυναίκα=a woman, ένα παιδί=a child.
Notice that physical gender does not (always) match grammatical gender.