As if/as though means in a way that suggests what the real situation is: She acts as though she wasn't warned. As if can also be used to emphasize a negative: As if I didn't have enough problems (= I have too many problems even now)!

the use of as if is hypothetical like if it seemed that the summer would never end. this summer is so hot and the heat lasts for long. she is crying as if someone hit her with iron. noone hit her but from her crying in this way, we say so

as if i knew the answer to that question :P

"As If" could be translated as "como si..." and a good example with be in the sentence: "As if it were the last time" that would be "Como si fuera la ultima vez"