Emoji and emoticons are related, but they are not the same. Emoji are standardized picture characters such as 😊 Smiling face with smiling eyes, ❤️ Red heart and 🔥 Fire.
Emoticons are typed from regular keyboard characters, such as :-) for a smile or ;-) for a wink. They were common before modern emoji keyboards became widely available.
Emoji can represent many more ideas than traditional emoticons, including people, objects, animals, food, places, flags and symbols. Emoticons mostly represent faces, gestures and simple moods.
Both are used to add tone to text. A short message can feel warmer, funnier or less abrupt when paired with an emoji or emoticon. See how do I use emoji for practical usage.