Should I calibrate a battery on macbook pro 2012? How it make correct?

Unibody Macs batteries (Late 2008 and newer MacBooks Pro) come precalibrated, so you don't have to do it yourself. If you want more information, read > http://www.apple.com/batteries/notebooks.html Do you have any problem?

Apple - Batteries

In some cases, calibration may damage the battery. I don't recommend you to calibrate the battery. To charge your computer, don't let it turn off: put your MacBook to charge before it turns off. Then, charge it until it reaches 100% or you see a green light in the charger. You can use your computer during charging

You are welcome

I've heard that once a month is necessary to calibrate the battery. Is it true?

Just to clarify, that used to be true, but it hasn't been true for a few years now. Modern MacBook Pro or MacBook Air batteries do not need calibration, and should not be fully drained if it can be helped. The link mende1 gave you will have all the details.