I am confused wher to ise if or where to use unless.

I think in sentence if the sentence starts its first line with unless and after comma it becomes negative then it is change of if + positive sentence to unless.

If is used as positive sentence, and unless is used as negative... Like... If you leave now you can the bus(positive)... Unless you practice you can't learn English(negative)...

If = in case of (positive) Unless = if not (negative) Ex..If you study hard , you will get first rank. Unless = unless you study hard ,you can't get first rank.