The Rav-Kav card is a pre-paid card that you can use for railways and buses.
When buying your Rav-kav card you must top it up with a minimum of 25 ILS Travel Credit. You can buy it in the Rav-Kav branches (link). You can buy credit online (for Android users only), ticket machines at the station or through the bus driver.
I personally don’t recommend paying for a monthly transportation plan because I found out charging money on a required basis cheaper.