The word here has more than one meaning in these sentences. Here is my ticket. It means my ticket is located in this place, such as a pocket. Here comes the bus. It means that the bus is arriving. (The bus is coming here.) Here they are. It means that they are located in this place. "Oh, my tickets, here they are in my pocket." Or, if they (friends, for example) are traveling on the bus, it means that they are now here. "Look! Here they are!" (They are arriving here.) Here it is. It means that it is located in this place. Here you are. If you just found someone you were looking for, you are saying that he/she is located in this place. "Oh, here you are! I couldn't find you." If you giving something to someone, you are saying, "I give this thing here (in my hand) to you" or, more simply, "Here you are." I hope this helps.

Here is my ticket. Here they are. Here it is. These three are used when you've been looking for something and you just find it. They can also mean: 给你。 Here you are. = 给你。 Here comes the bus. = Usually said at the bus stop. If you can see the bus coming you say: "Look. Here comes the bus." （快来了）