"I eat bread" vs "I am eating bread"
In English, I can say "I eat bread," which suggests a general habit in my current life of eating bread...or likewise, "I shop at Walmart." Here it does not mean I am presently eating bread, or that I am at Walmart at this moment, but vaguely suggests a habit of mine.
On the other hand, I can say "I am eating bread," or "I am shopping at Walmart." These do suggest I am immediately in the act.
How do we distinguish between these in French? Do the following two sentences properly address these different tenses?
"Je mange du pain." ou "Je suis manger du pain."
In French, there is no être + [gerund] form for the present tense. There is only (for manger, in this case) “Je mange” meaning both “I eat” (habitually) and “I am eating” (at the moment).
You would distinguish between the meanings with context.
If you really want to emphasize the “nowness” of what you are doing, you could say “Je suis en train de manger.”
French has a gerund form as well (mangeant), but I am not sure that the construction (je suis mangeant) is even grammatically correct or not - at the very least it is unheard of and awkward.
But one of the things that you come to realize about English is that from almost every other language, the frequency of the use of the gerund form in English is a little weird. We have made a more complex form of the present the default at the expense of the simple present, which has been shuffled to do the work of something like 'd'habitude'. Best to shed the idea that the 'is running' construction is somehow normal.
In terms of actual usage, one would be far more likely to hear 'en train de' than the gerund. The gerund is reserved for some fairly specific uses like 'seeing the danger, I ran'.
Please note that "Je suis manger du pain" is incorrect. The answer to your question is that, in the present tense, French verbs mean three things: 1. I (ex. run)... 2. I am (ex. running)... 3. I do (ex. run)...
All three translations are correct, and there is no way to tell which one is indicated without context (knowing the rest of the conversation).