sama sekali mean completely, at all, totally, entirely. usually use in negative sentences : S+ negative Verb + sama sekali or S+sama sekali+ negative verb example: saya tidak mengerti sama sekali (I totally don't understand) or saya sama sekali tidak mengerti they have same meaning.

Sama sekali is equivalent with at all or totally or completely. It can be at the end or in the middle of the sentence. For instance, I don't know how to swim at all = Saya tidak tahu cara berenang sama sekali. I completely don't understand about what you are saying = Saya sama sekali tidak mengerti apa yang kamu bicarakan. :)