The terminal near downtown Buenos Aires is very modern and like a small airport or cruise ship terminal. There is a baggage check in area, a nice area with tables, a snack bar, and a couple of shops.
When we entered the terminal there was a schedule of trips on the wall and an information booth. If you are going to Colonia there is the choice of a one-hour Buquebus or a three-hour ferry trip. The 3-hour one is, of course, a lot cheaper, in fact almost half the price. At the Ventas line you tell them which trip you want and show your passport. You have a choice between first class and tourist class. You then go to pay at the Caja (cashier) and are issued a ticket. There is a booth next to the Ventas where you can change Argentine pesos or US dollars to Uruguay pesos.
There is an area to check luggage but most people just had carry-on. We were given a boarding pass and then went through immigration. Immigration officials from both countries are surprisingly in the same room. We obtained our exit stamp from the Argentina side of immigration and were then pointed towards the Uruguayan immigration official in the same room who gave us an entry stamp. That way once you get off in Uruguay, you don't have to queue to enter the country.
Once we entered the departure area, we noticed people were lining up to board even though there was still 45 minutes to departure. Since there are no assigned seats you line up to get the best seats. There is an enclosed walkway to the ferry, and on board we were pleased to find the seats are like airline seats but much bigger and with plenty of leg room. They also reclined nicely. There was plenty of room to store your carry on under the seat in front of you. In the back there was an area with a few tables. There was a snack bar that sold sandwiches, soft drinks, coffee, tea, beer, wine and pastries.
Once we were underway, a small duty free shop opened. They were selling perfume, alcohol, cigarettes, and candy. The cigarettes and alcohol, especially American whiskey, seemed to be hot items.
The trip over was relaxing except for a noisy group of soccer supporters who were going to support their team but who in the process disturbed everyone else of the ferry. It was easy to move around even though the ferry was virtually full. The weather was calm so there were virtually no waves, just a gentle rocking. On the way back we had an even larger vessel which was almost like a small cruise ship. The whole exercise was pleasant and quite efficient.