The very first thing you need to do is get a SUBE card. What is it? Well, this plastic thing. 
You will need this magnetic card to pay for all public transport in BA. Without it you will not be able to pay, so getting this card is vital if you want to take a bus or the metro.
We were used to pay tickets with coins because the ticket used to cost less than $1 (argentine peso), but nowadays coins are useless because of the devaluation, the government decided to install a new system to pay transportation in the city. This is when the SUBE card was invented, a card to pay buses, subways, trains and even highway tolls.
