Merhabalar arkadaşlar

I have a question about the meaning and usage of the following 

bari, en az, hiç değilse, meğer

and others that I´ve been hearing in the series that seem (at to me) to have the same meaning as at least, apparently. So do they all mean the same and when to use each and how?

Şimdiden teşekküer ederim, hem de çok.