Translation:We walk for approximately an hour.
https://sun9-29.userapi.com/c858228/v858228559/192618/Ele2spkDX9E.jpg You have missed the space, as I see
Have been walking is the present perfect tense as opposed to the simple present, which is used here in both Greek and English. The perfect tense implies that you were doing and still are doing something (like walking). The simple present can be used much more generally: What do you guys do on the weekend? Well, we walk for about an hour. What do you do to exercise? We walk for approximately an hour.
I would say yes. There is no present perfect continuous ("have been walking") in Greek, only present perfect simple ("have walked"). The problem with the present perfect simple is that it implies that the action has finished right now, whereas the continuous means that we are still walking. Έχουμε περπατήσει conveys the same "finished, completed" meaning, so I would translate "We have been walking for about an hour" as "Περπατάμε για περίπου μία ώρα", to maintain the meaning of ongoing action.