The official language of Argentina is Spanish, so if you speak it then awesome. Most people here don't speak any other language, and only a very small percent of the populate are fluent in English.
That said, if you only speak English, you shouldn't have too much issues getting around the country as people that work in tourism and hospitality all have great command of English
Also, in major cities and especially posh neighborhoods like Recoleta and Palermo in Buenos Aires, many younger generation can speak decent English, so if you need to ask for help they should be able to. Most local businesses like restaurants in these areas also have staff that can communicate with you in English
By the way though, taxi and bus drivers rarely speak English so unless you're going to a major landmark you should write down your destination on a piece of paper or your phone to show them. Supermarket workers don't usually speak English either. Basically any services that are mostly used by locals everyday won't have staff that speak English
In regions with many tourists like El Calafate, more people can speak enough English to help you with basic questions
At the end of the day it's best if you learn at least a few phrases in Spanish, but don't worry about not being able to get around the country if you don't speak any Spanish. Have something like google translate on hand with you to help you out could be really useful