It has many meanings. It’s generally used as exclamation. For example, if I’m a group of friends one friend made a funny, lighthearted remark about another member in the friendship group, everyone else might say ‘eyyyyyyy’ to show that they found the joke funny. It could also be used when something positive happens to show excitement or pleasant surprise. For example, if you were to get a promotion at work, your friend might say, ‘eyy well done you!’. It is an informal way to show your emotions.