I'm not that guy, but I can speak to what you're asking. I've followed Wendelstein 7-X for almost a decade.

Nuclear fusion occurs at extremely-high temperatures. As you heat your fusion fuel to sufficiently-high temperatures to allow fusion, the matter transitions into a plasma, which is great: plasmas react to electromagnetic fields. As such, a major challenge with achieving viable nuclear fusion is making a vessel capable of holding the fusion reaction. Because we can't create on-demand gravity wells, the next best option for confinement is using electromagnetic fields to hold the plasma in the air.

So, you now have an "electromagnetic bottle" capable of suspending a fusion reaction above the reactor's walls. Now, you have another issue: how do you ensure the fuel will sufficiently mix to sustain a fusion reaction? One approach is to move the plasma in a loop. The topologically-simplest method to accomplish this loop is the torus. Such a plasma-confinement device is called a tokamak. A tokamak uses two magnetic fields, torodial and polodial, to accomplish its task. The torodial field is driven through the plasma to push it forward, while the polodial field pulls the plasma in toward the center. Proper balance of these fields will allow the plasma to circuit the vessel following a helical path, achieving confinement.

However, driving two separate magnetic fields is energy-intensive, and a successful fusion reactor will want to minimize its own power consumption to maximize the amount available for external usage. Enter the stellarator. The stellarator also drives the plasma around in a circle, it but uses a single magnetic field. How? It "tricks" the plasma into "thinking" there's only one magnetic field by using computer-optimized magnets with highly-complex geometries. This provides stellarators with a major engineering advantage over tokamaks and is a primary reason Wendelstein 7-X would have chosen it.

With the confinement vessel topology largely identified, the next main step is to figure out how to build a vessel able to contain a sustained fusion reaction. For context, fusion experiments traditionally only operate on timescales of milliseconds to maybe a second. The reason? Fusion occurs at millions of degrees, and keeping the reaction vessel cool, ensuring a continuous supply of fuel, and dealing with reaction "exhaust" (e.g., alpha particles) and stray high-energy neutrons from the common deuterium-tritium reaction (which irradiate your reactor walls because neutrons don't react with electomagnetic fields) is a major, major engineering challenge. Any operational, net-positive fusion reactor must be able to operate for days, weeks, and months on end.

What Wendelstein 7-X has been attempting to do for years is demonstrate that building such a vessel is even possible. Their overall goal is to sustain a fusion reaction for about 30 minutes. Such a timescale will show a proof-of-concept system which enables sustained fusion reactions to occur.

Currently, the preferred fuel is deuterium-tritium because the fuel is generally available and has an attainable fusion temperature. The stray neutron issue can be mitigated by lining reactor walls with lithium to breed tritium fuel. Even better is to use the helium3-helium3 reaction, which completely annihilate to produce pure energy as the output (welcome to e=mc^2, enjoy your stay). The main holdups are: (1) the reaction occurs at much higher temperatures than deuterium-tritium, and (2) he(lium)3 is quite scarce on Earth. Once Wendelstein 7-X shows how to engineer a proper confinement vessel at a "lower" temperature, you can then work on the higher temperature levels required for he3-he3. Also, he3 is plentiful on the surface of the moon, so mining the surface of the moon will be performed to obtain the required fuel, which is the fundamental premise of the movie "Moon".

Someone asked for information on electromagnetic plasma containment folding. I recommend reading up on magnetohydrodynamics (MHD). It's the mathematical and physical foundation of your interest.