You need to speak english with english rules and french with french rules.

There are two possible ways to make the present tense in French. The simple present and the "être + en train de + infinitive" form.

If you want to say "I'm eating", you can say :

-Je mange

-Je suis en train de manger

The first form can be used whenever you want to translate present tenses. The second form is used to emphasize the fact that you are doing it RIGHT NOW.

Let's say you have a friend that suggests you to go to the cinema but you are working. To emphasize the fact that you are working and cannot go to the cinema with him/her, you will use "en train de".

-Viens, on va au cinéma. (Come, let's go to the cinema.)

-Désolé, je ne peux pas, je suis en train de travailler. (Sorry, I cannot, I'm working.)

Mange means "is eating" or "eats". you dont need to put "est" in there because it is already covered by mange. hope this somewhat helps!

becuase there is no such tense as present continious in french we just use the present to refer to it

Mange translates to either 'am/is/are eating' or 'eat/eats'. Therefore you don't need another word in there for 'is'

In English, we can say 'the cat is eating a red apple', or 'the cat eats a red apple', and they have just slightly different meanings. In French, however, 'mange' can translate to 'is eating' or 'eats'. I hope this makes sense?

mange (or any other forms of this word) may be translated as "eat", "eats", or "is eating", same with some other verbs :)

and I almost forgot about the en train de, that's when you want to emphasize that the action is being done like right now

i've never thought about that. Good question. I guess there are just different ways of talking languages.