Question: I don't understand the concept of majors. When choosing colleges, should we select those that have all the majors we're interested in, or just one?
This "major" issue can be confusing indeed ... and sometimes even a "major" pain. :-) When you apply to some colleges, you need to have a major in mind and then you must apply not only to the college itself but also to your specific major or program. Sometimes, you may not need to choose a major, but you do need to apply directly to a specific "school" within a university (e.g., "School of Education," "School of Allied Health Sciences," etc.).
Whenever you apply to a college that asks you to list your choice of major on your application, be sure to find out if that choice is "binding." That is, ask admission officials if you can switch your major as soon as you enroll, if you so choose. At some places, it is hard to make a change once you've committed.
Not surprisingly, many high school seniors do not know what their college major will be and--even those who do--often want the flexibility to change their minds. Luckily, most colleges don't require you to commit to a major at the time of your application (though many WILL ask what your possible major or primary areas of academic interest might be).
If you do have a major in mind--or more than one--then it certainly makes sense to apply to colleges or universities that offer these options. Some majors--like biology, psychology, English, history, etc.--are so very common that nearly every institution (except the more specialized ones) will offer them. However, there are also unusual fields (e.g., "Soil Science," "Recreation Therapy," "Jewelry Design") that won't be widely available. So, of course, if you think you may be interested in an atypical field, then you would be wise to consider only those colleges that offer it.
Keep in mind, however, that--in most cases--a college major is made up of only about 10 to 12 courses, and most college students take about 32 courses during their four undergraduate years. (Requirements vary from major to major and from college to college, but those are ballpark figures.) So, even once you've determined your major for sure (which may not happen until the start of your junior year), you will usually have lots of opportunity to take classes outside of your major field.