In which context? Do you mean something like 'etwa eine Stunde' and 'über eine Stunde', with a number after it? In this case: 'etwa' - about, 'über - more than.

If you looked up "about" and found these two choices, the way to get a feel for the meaning is to do a "reverse lookup" (i.e. look up English/Farsi terms for both choices). E.g. on Pons: http://de.pons.com/%C3%BCbersetzung?q=etwa&l;=deen∈=&lf;=de Meaning 1: "ungefähr, annährend" = about, roughly, more or less This is an ADVERB. http://de.pons.com/%C3%BCbersetzung?q=%C3%BCber&l;=deen∈=&lf;=de This is a PREPOSITION, and prepositions don't translate well between languages. The base meaning is "in a vertical higher position" or "crossing something", so you get "above, beyond". But it can also be "about a subject" ("über ein Thema"; picture someone looking down at a subject), or it can mean excess ("über eine Stunde" = more than one hour, over one hour; picture something overflowing).