How to recover partition on my mac?

I have no idea why partitions on my mac disappeared. Maybe it is overwritten or damaged by a virus. I have spent all day searching the internet for solutions. Much software is suggested to help and I chose Nice to Recover Data for Mac. Frankly speaking, it can truly recover the partitions and the data on them but I can open them. Anything I did wrong with it? How to use it properly? Can anyone tell me?