An API is an interface to communicate with,usually we saw that in the server with the form of endpoind (I'm talking about REST), the server will be connect to a database where you have ... data.
YOur objectiv is to get data about corona so your front angular will have to get data, since you cannot directly interact with database that's not your's will ask an API some data -> in tech you will make a request on an endpoint like (https://thismyurl/allcovidvalue) <- (fake url) and a serveur will respond.
You have to find an api that have data about corona and a public API (free to use so)
To do it in angular I recommand to use HttpClient