'If you asked me now' or 'If you ask me now', which one is correct? I saw people use both of them so if both are correct what is the different? (I use English as a second language so sorry if my English is not so good.)
You have heard both used because both are grammatical. Check out this page for an explanation of the different ways to phrase a conditional statement in English.
Consulting this page, in particular, the first example you list, "if you asked me now," is Type 2 Conditional, and the second, "if you ask me now" is either Type 0 or Type 1, depending on the rest of the sentence.