Yes, Memtest86+ will test your memory, you should run it at least overnight to get better results. In rare cases, some errors can slip past, but it is not often. A longer test time is always a good thing.
what will memtest86+ scan?, if there are some problems what shall i do, and how will i know what kind are they?
It simply scans for abnormalities within your memory, if errors pop up, you must simply replace the bad sticks. Memtest will display errors in memory for you to see (they'll be in red), and once you see those you know there an issue.
You can use cpu-z(or the memory makers specs from the website) to see how much is needed for most sticks. Memory is getting better so more and more just requires 1.5 volts(this is the default for DDR3)
Memtest+ to put it simple just places a data set into memory then reads it back if it does not match, the memory has failed. It will keep going and just keep adding errors as it finds them.