Fear about what to say to a griever is common. Most people are uncomfortable around someone who is grieving because they’re afraid of saying the wrong thing. Since they have no idea what to say, often they simply choose to avoid the griever.
The most important thing anyone can do is to let the person who is grieving know that you care. Give them a hug, show them your concern for what they’re going through, and tell them you want to help (and mean it)!