Near the bottom-left corner (it can be slightly higher in some situations), there is a panel which has a few tabs. By default, it will usually show the recent happenings in the game. This should help you to find it. You can switch to the ‘World’ tab to chat. It has some other options like ‘team up,’ for when you are in a multi-player dungeon or such and wish to co-ordinate with team-mates (or tell them to click ‘ready’). Alternatively, you have a ‘faction chat’ room once you gain factions. If someone is added to your ‘friend list,’ you can have a private chat with them. Or you could marry, although recall that, “Marriage is a three ring circus: engagement ring, wedding ring, and suffering.”
That’s if you were asking for how to speak with other players. The question was slightly vague. At the least, this might be of interest to other players who are curious about this – I’m not sure that all of these chat options are clearly pointed out early in the game.