Buenos Aires has a very good public transport service, you should avoid the rush hours o weekdays. Bus, trains, and subways use a card called "Sube" and it's the only way to use the public transport. You can buy Sube card in many places, but we recommend to buy at any subway station. The sube card costs around 1,25 usd. You can also buy a sube card on the lottery houses but they usually have higher prices. Sube card comes with 0 Balance, but it allows to have negative balance. We recommend to charge it with 10 USD for a week of normal usage.
How to use the bus?
When you get on the bus the first thing you need to do is to tell the driver where you will go, then you put the sube card in a yellow box to pay for the trip. Wait for the ok on the yellow machine and you re ready to go. If you don't know Spanish try to show to the driver your cell phone with the name of the destination. Every bus has a number and each number corresponds to a route on the city. Some buses with the same number could have a branch on the route, so there is also a sign with colors. Here is an example of a bus on Buenos Aires:
In red circle you can see the branch of the bus, usually you don't care about the brach. The goverment application tells you which branch to take. Branches are usually used when you go outside CABA.
How to use the subway?
On every subways station, you will find windlasses and you just need to pass the card on the reader.
How to use the train?
On every train station, you will find windlasses and you need to pass the card on the reader. The only difference with the subway is that you will need to pass the card again on the destination. Make sure to always pass the card since some train station could be tricky.
How to know which bus/subway to take?
The government has an official travel application that is very useful to know which bus number to take or which subway. The application also takes into the account if the subway has problems and suggest to take a bus. You can download the application called BA Como llego