One of the first things you'll notice when you come to Brazil is the word mesmo floating around here and there, apparently with no concrete meaning. Well, it's not one of those words that can mean almost anything depending on the situation - mesmo in Portuguese has just a few common usages. Let's review:
Is that really true; Is that a fact; Isn't that something.
You get the idea. MESMO is conveying emphasis here.
Emphasis again. Here we see it can mean really -- just like muito works. But watch out because you Brazilians would never say for example: "É mesmo bom". They would always say "É bom mesmo". I don't know why. More examples:
É ele mesmo! / Eu sinto bem mesmo! / Sou eu mesmo (a)!
Watch out! This mesmo que always triggers the (present) subjunctive. Why? Well, that's because this sentence is a (supposedly) hypothetical -- it has not happened yet. I would argue otherwise, but there are simply some grey areas of grammar rules that are not consistent. I wrote another post on the present subjunctive that gives more examples. Even more great examples can be found on Linguee.pt.
Mesmo also means the same. Pay attention as in this usage it takes a gender ending to agree with the subject. For example:
É a mesma coisa. / Vamos almoçar no mesmo lugar.
* the pronunciation varies quit a bit for this word but the coolest is to say it: MEZHMO