What is Bootstrap?
To add to your build a house analogy...
If paint for your walls is CSS, giving the wall a class of "midnight-blue" delivers a pre-mixed bucket of paint from Home Depot right to your home and paints your wall. Need to level a picture? Just make sure your wall has a class of "level-photo" and, BAM, you're pictures are straight. Don't know how to make textured tile in the bathroom ? Just name that tile "texture-sexy" and your tile goes from smooth to "oh so fancy" in no time. No masonry experience needed.
Bootstrap can save you tons of time aligning, sizing and helping your page be responsive. I find this is usually most handy when I'm focused on function over styling. I can say "text-Center" or "img-responsive" and things just line up nicely. I can then spend my time on the finer things. Like making stuff work.
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