I was reading different article on the best surround speakers to buy and most of them said to buy the surround speakers that are bipole dipole speakers. How are these type of speakers different from other surround speakers?
Bipole and Dipole speakers are not the same thing, so rid yourself of that idea. Bipole and dipole refer to very different types of speakers.
Most speakers that you see are sometimes referred to as "monopole" speakers. The typical speaker as one or more drivers mounted on a baffle, and this is typically mounted into a box, which provides back pressure, greatly increasing the efficiency of the speaker drivers. It is called a monopole as the drivers face one direction and the sound projects into that direction.
A bipole speaker projects in two directions, equally. A Magnepan planar speaker is a mylar driver stretched over a wooden frame. Since there is no box, the mylar panel vibrates and projects its sound in two different directions at once. In a more typical bipole arrangement, you might have a box with mirror sets of drivers pointed into different directions, usually in opposite directions, or at least close to opposite. An excellent example of a bipole speakers is the PSB Image 10S, in which a matched pair of drivers are mounted on identical baffles, and angled at approximately 90 degrees from one another. Using two panels provides a much wider soundfield.
Dipole speakers are just like a bipole, with two sets of drivers, but the different driver panels are wired out of phase from one another. The purpose of wiring them out of phase is to create an even wider soundfield than bipoles provide. Wired out of phase creates a null field around the speaker where the sound cancels out, but the overall soundfield is even wider, and the cancelled out area around the speaker itself makes pinpointing the speaker difficult. I think the best example of a dipole are the surround speakers from Paradigm, the ADP line of speakers.
To me, there is no best answer of what makes for the best type of surround speaker. Each of these types of speakers represents a different solution that may or may not be right for your room. Personally, I use monopoles, but as much for convenience as performance. You should look into all types of speakers for your surrounds to see what works best in your room.