Most long English words are not single blocks of meaning. They are built from smaller parts, and many of those parts repeat across hundreds of words. Learning a root is therefore not learning one word; it is buying a key that opens a whole corridor of doors.
Take 'spect', from a Latin word meaning to look. Inspect is to look into. Spectator is one who looks. Retrospect is looking back. Prospect is looking forward. Once you notice the root, an unfamiliar word like 'circumspect' becomes approachable: 'circum' means around, so a circumspect person is one who looks around before acting, in other words, cautious.
Consider 'dict', meaning to say. Dictate, predict, contradict, verdict, dictionary. Or 'port', meaning to carry: portable, transport, export, import, porter. Or 'scrib' and 'script', meaning to write: describe, manuscript, inscription, prescription.
Two more worth knowing are 'cred', meaning to believe, and 'aud', meaning to hear. Credible means believable. Incredible means not believable. Audible means able to be heard, and an audience is a group that hears.
The method is straightforward. When you meet a long unfamiliar word, cover the prefix and the ending and look at what remains. Ask whether the middle resembles a root you already know, then check whether that guess makes sense in the sentence. Context confirms or corrects the guess; the root gives you somewhere to start.