As pertains to people, you only "know" someone (i.e., are acquainted or familiar with them) once you've "met" them. I think your confusion might stem from the fact that "conheçer" is used for both in Portuguese ("muito prazer em conheçer você" - "very pleased to meet you"). "To meet" here only refers to the first time that you encounter someone (or, more rarely, something). I say "here" because you also use the verb "to meet" for meeting up with people (numa reunião, "I met my friend at the restaurant"). As I touched on at the beginning of this answer, English also distinguishes between levels of social familiarity. So, you wouldn't typically just meet someone for the first time and say that you "know" them, because knowing implies a deeper level of familiarity, like with a friend or someone you've met with many times already. For new people, it's more accurate to say that you're acquainted with them (i.e., they're an acquaintance). The difference between "to know" and "to recognize" is similar - the former implies more familiarity, the latter lesser familiarity. There are also other languages (I'm thinking of ancient Greek here) that are more precise than English in regards to defining forms of knowing, and in fact Portuguese (and German, too) both have saber/conheçer (in PT) and wissen/kennen (in DE), whereas English usually just sticks with "to know". Note, though, that many native speakers don't strictly adhere to what I've just told you. It's common to hear someone say, "Oh yeah, I know him", because you don't usually need to specify how well you know someone.

Reading ,u know all.