OS X actually allows you to install Windows directly onto your hardware and boot into the operating system using a feature called Boot Camp. If you've ever run a dual-boot PC then this process will be familiar to you.
There are pros and cons to running Windows on your Mac using Boot Camp.
My method of choice for running Windows on my Macs is to run it inside a virtual machine.
While there are free tools that allow you to run Windows on a Mac - such as VirtualBox - this is one time when I recommend buying commercial software.
My software of choice is Parallels Desktop. It's fast, reliable, easy to use, and offers a number of features that make running Windows on a Mac a more streamlined process. It also features performance tuning that allows you to optimize your virtual machine depending on the workload.
Also, you can use Parallels Desktop to run a whole host of other operating systems on your Mac, from Linux to Google Chrome.
A license starts at $79.99.
If you already have a PC running Windows, you can access that remotely via your Mac, and this will give you access to all the data and applications on the system.
This is a program - actually, it's a compatibility layer, but that's rather a mouthful - that has its roots in Linux, but also works on OS X. Wine is far from perfect, and can't handle every Windows app, but it still offers pretty broad support for a whole range of Windows applications.
Wine itself doesn't offer an OS X download, but the third-party application WineBottler brings everything Wine has to offer to the Mac. And best of all, it's free.
WineBottler is fully compatible with OS X 10.11 El Capitan.
Prefer a commercial application? No problems. Take a look at CrossOver for Mac. Not only is CrossOver compatible with thousands of Windows applications, but you can also try installing unknown and untested Windows application into it. Many times they just work, and those that don't work perfectly might work well enough for your purposes.
Subscriptions start at $40, and there's a free trial available so you can test it before committing.
One of the most frustrating things about switching between OS X and Windows is remembering which gestures you can use on which operating system, and at no time is this more of a headache than when you're running Windows on a Mac.
The problem is that because you're running Windows on the same hardware as you normally run OS X on, you expect everything to work the same, and that includes the trackpad. But it doesn't, and this is something that can be infuriating and highly unsatisfying.
Enter Trackpad++, a utility that is basically a third-party Windows driver (supports Windows 7 to Windows 10) for Apple's Multitouch and new Force Touch trackpads found on MacBooks. Not only does it support 2, 3, and 4 finger OS X gestures, but it also supports Windows gestures, and has the ability to detect and ignore accidental touches of the trackpad.
This is the closest you're going to get to having the full Mac trackpad experience while running Windows on your Mac.
If you're looking for a driver that offers support for the Apple Magic TrackPad, then you should take a look at TrackPad ExtraMagic, also by the same developer.
Both Trackpad++ and ExtraMagic are donationware, which means that you can use them for free, however unless you buy a license you'll have to update the driver regularly. I happen to think that if you run Windows on your Mac using Boot Camp or you use the Magic TrackPad on a PC then this software is easily worth $15 to $20 for a license. Once you have a valid serial code then there's no requirement to update the driver regularly.
In order to run Windows on your Mac either through Boot Camp or in a virtual machine using a program such as Parallels Desktop, you will require a valid Windows license. Specifically, you will need a full version, and not an upgrade or OEM version (an upgrade version would only be valid if you were upgrading an existing copy of Windows that's already on your Mac).
Full versions of Windows 10 are $119 for the Home version, and $199 for Professional.
If you are already running Windows 7, 8, or 8.1 on your Mac, either through Boot Camp or in a virtual machine, your copy of Windows is eligible for a free upgrade to Windows 10 (but hurry, you've only got until July 31st to upgrade).