You can add things to words in Esperanto to have them have different meanings in a similar fashion in which you can make act into actor, teach into teacher or lingua into linguist. But, unlike in English, where you have or, er, ist and others suffixes, in Esperanto you always use ist as your suffix for professions or hobbies.
The Esperanto suffix which shows a profession or a hobby is ist. You add that ist right before the ending of the word.But wait a minute - what is the ending of the word? Well, it's simply the last one or two letters of the word which indicate to which class the word belongs. The ending for nouns, for example, is o, and all nouns in Esperanto end in o (even the word Esperanto itself ends in an o). This makes it really easy, but don't worry if you don't fully get it yet - we will learn more about this later.
Let's try to apply the ist rule. For example, if the Esperanto word for piano is piano, and we want to make it into a pianist, we add ist right before the ending o and we get pianisto.
So, if a language was lingvo, and its ending is o, how do you think you would say a linguist ?