A fundamental rule of good writing is to show, not tell. Saying “He was angry” is telling. Saying “His eyes bore into his opponent like steel rods, fists clenched at his side” is showing.
Showing is especially important in rendering emotions, which are essential for sucking your reader into the story. Some emotions are anger, love, hate, betrayal, disappointment, grief, heartbreak, and so forth. These words are okay to use in your first draft, but when you start to edit, stop and consider how you can describe what the character is feeling instead of taking the easy way out. Aim to avoid using that word entirely, but to render it in such a way that the reader knows exactly how your character is feeling at that point in your story.