This is an interesting question, and the answer depends where in the UK the person comes from. In the north of England, 'tea' can sometimes refer to the evening meal which families have at home. This is particularly common among the older generation and more working-class families. So if someone from Yorkshire, for example, invites you home 'for tea', this could mean a full evening meal at around 6 pm. However, for most British people, 'have tea' means meeting some time between 3pm and 5pm, either in someone's home or at a tea shop or cafe. You'd just have a cup of tea, and probably something sweet to go with it, such as a slice of cake. Some traditional tea shops serve quite elaborate 'teas' with sandwiches, cake, scones, jam and cream, but this is becoming less common. I suspect that your friend was using the second meaning of ' have tea', which is more common and widespread. I hope that helps.

You are right with your guess: it means 'drink some tea together'.

Yep, the other replies are good. I would also say 'to have tea' represents a meeting as well and a pleasant occasion - perhaps a time to have a chat....