An accent is mainly about pronunciation: the sounds, stress, rhythm, and intonation someone uses when speaking. A dialect is broader. It can include pronunciation, but also differences in vocabulary, grammar, and how language is used in everyday situations (for example, what counts as polite).
So if two people speak different dialects of English, they may use different words, different grammatical patterns, and different pronunciation. If you are talking only about their accents, you are pointing to the pronunciation differences. Everyone who uses a language has both an accent and a dialect; neither term means someone is speaking incorrectly.
Source: Duolingo — Dialect vs. Accent: What’s the difference?