The yellow tourist bus (Buenos Aires Bus) is a Hop on Hop off bus with more than 3h pure bus ride. The route mainly covers the area of the city center, Palermo, port and La Boca. In total there are over 20 stops.
The buses run at regular intervals and you can get on and off as you wish. During the tour (subject to route changes) you will pass the iron tulip Floralis Generica, the Obelisk, the famous La Recoleta Cemetery, the Boca Juniors football stadium and other highlights.
Changes of the route are possible, so please check the website for the current route. You can also find information about the prices there: https://www.buenosairesbus.com/recorridos-ar.php?id=3&lang=en
The buses are large double-decker buses. In the bus itself there is a headphone jack at every seat. You can choose from different languages and an audio guide gives you short information about the sights on the way.
The bus is very nice to get an overview of the city. I didn’t really use the hop on hop off possibility very much, because you could spend a lot of time at most of the stops. You should use it as an overview tour and limit yourself to a few exits. Taxis are cheap and you can take them on another day to go to places where you want to stay longer. For example, I only drove through La Boca because I wanted to go there again anyway with time and for a freewalking tour.
There is also a second provider (Grey Line Argentina) of Hop on Hop off tours. This one has red buses. You can find more information here: https://graylineargentina.com/tours/buenos-aires/buenos-aires-citybus-hop-on-hop-off-6678_299/