Along with How to Cook an Egg, this instruction is perhaps one of the most basic. Between the water and the heat source one must contain the water so as not to extinguish the flame. Primarily this must be done in something which will not burn or break in the heat or otherwise self-destruct. Additionally, there must be enough heat to bring the water to a boil. This may seem obvious, however, one can observe at higher altitudes that a small camp fire may NOT be adequate. The addition of a small amount of salt should remedy this problem. Then again, water might not be PURELY water, as in the case of broth, pasta water, tea, shrimp boil, etc. In which case it very similar and tangent to boiling water, but not exactly so. Then there's the issue of where the water is sourced from. That might be an additional need for boiling water, and in and of itself may or may not make water potable. Beware.
Now, I am aware that the Original Hansen Family Cook Book has an entry titled: "How to boil water" and it's not my intention to transgress against scripture in any way, further it is also not my intention to suggest or impugn, any lack of seriousness or frivolity on the part of the original post, posted, poster, or postee, as the case may be. However.
Further, one of my most embarrassing moments in my lengthy though often part-time career as a cook, was when I was instructed to make a roux. Now, I knew how to make white sauce and the general idea of making a roux, I just never knew the term: "roux." (interpret this comment as referring to the thickening of watery juices, etc., et al.)
Now, what one must consider is that water is not the only liquid medium in which to cook foods, however, if kept just around the boiling point, it cooks them at about 212 degrees f. Which is useful, because it becomes a kind of constant, so that if you were to add rice, from say, the same quantities, varieties, and sources, it will always cook at about the same rate and at about the same time. Or potatoes. Boiling oil must be mechanically kept at about 375 or 425 or whatever, I can't remember. The problem is, that water tends to dissolve food, whereas, frying tends to lock flavors in. This is why boiling water becomes the medium of choice for, say, beans, grains, pasta, herbs, or other dehydrated ingredients.
The possibilities are endless. As could be this post, were I to "try my luck" at it. But enough is enough. Concise and clear, as they say.