Before you become set on your phone antivirusremember, antiviruss are different (different in quality, in fact, they are paid or free, and much more). If you install the free version, you can use a limited set of functions or the period of use of the program will be limited (some antiviruss, for example, the virus, the period of free use is one month).
Also, don't forget that antivirus can be installed only one. Also remember that antivirus from time to time needs to be updated (otherwise the use of such antivirusand not will).
Purchase antivirus you can online, paying by Bank card (can be virtual) or e-wallet. Once you have downloaded the software you want, install it into the phone (move the program file to the phone's memory through usb cable or bluetooth). After the antivirus will be in the phone, install it by selecting the corresponding item in the menu.
It is better to purchase an antivirus on official websites or in specialized stores, and not on third party sites that can easily become a victim of fraud.