As the title suggests I was reading on the minecraft wiki that you are able to merge minecarts. Firstly how is this done I don't quite understand the wiki and are you able to merge a storage cart with a passenger cart into one?
Well I haven't played minecraft in a while but, by looking at the wiki page I can tell you a few things. By my understanding of merged minecarts there are two possible ways of being able to do this.
You can create a train. This is done by having a powered cart at the back of x number of carts in the direction you want to go in.
(X)= powered cart,
()= carts (Just imagine that they are on tracks :P ):
(X) () () () ------->This is the direction you want to go in.
The powered minecart on the back pushes all the carts forward as it is on the back. You can't pull with minecarts in minecraft as mojang have not built this function in to it yet. However the drawback to this is that it isn't merged but still does the same job and is effective. Also you can have a passenger cart, a storage cart and any other cart pushed along the track at the same time. (Video Link Demonstrating it)
To my understanding to actually merge minecarts what you want to do is have a track going up a hill. You then have one cart positioned at the bottom of the hill (Bottom track should be on a straight surface. Make sure it is only one track long at the bottom of the hill) with a block at the end of the straight track. You then want to feed all the minecarts from the top of the hill down to the bottom. This should then hopefully merge your minecarts together. You can also merge any type of minecart together (So yes you can have passenger cart with storage cart). Although I'm not too sure on the amount of minecarts that you can merge together. By reading the wiki page it says 3+. However there is a drawback and that is that you can either get stuck when turning tight corners and then you will ruin the whole merged carts and you are a lot slower than a powered cart pushing other carts.
I know its a long answer but that the best way that I can explain it to you. Sorry ;)