Virtual reality is a new revolutionary technology with one major problem. Your room is only so big and so you can only walk so far before you run into one of your walls. The virtual world could be infinite but the real world is still limited by the range of your headset and the size of your room.
There are a few creative solutions that developers have come up with to this problem ranging from pieces of hardware to in game mechanics. One solution for those who don't have to worry about space is to have a special IR tracking camera that can track over large distances (we're talking about a football field) and just simply have a warning for when you approach the boundaries. This allows for a larger operating area and the user would rarely run into a boundary. However, since most of us don't own a football field of empty land this solution isn't practical for most people.
Another hardware solution has been to develop a sort of treadmill system which allows for users to walk on a sort of platform with ball bearings. What this does is simulate the feeling of walking without having the user actually go anywhere. Examples of this include the Caminator VR and the Virtuix Omni. However, this solution is expensive and looks ugly to store in your house.
Software solutions to this problem, while not as awesome as football field ranged IR cameras and treadmills mounted on ball bearings, are far more practical. The most obvious software solution to this problem is to simply use a sort of controller to manipulate movement. This solution isn't bulky at all and most VR headsets come with a sort of controller so it comes at no extra cost.
Then what was the point of this post if the solution is so simple!
Well, the solution isn't so simple. The problem with controllers is that many people get motion sickness when they use them for manipulating movement. While our brain sees that we are moving, it knows clearly that we are standing still. This confusion can cause motion sickness for a lot of people and is a major block in making VR mainstream.
Some developers have come up with clever tricks such as needing to swing your arms back and forth to manipulate the movement of your character. These methods help with motion sickness since your brain is at least somewhat convinced that you are moving (though it still knows you are not going anywhere).
Until a be all end all solution is found for this problem VR will always have a major barrier between it and mass popularization. Thankfully there are many developers from many companies who are looking to solve this problem once and for all.