When you speak of "container" is a fairly broad term, personally I do not know if you refer to the container of the same element or of which it is contained.
Container of the same element:
For example, if you hit F12 and select these paragraphs, you will see that my words are "contained" by a <p> all tags contain something, for example:
<section> <div> <p> hola </p> </div> </section>
Although it is also true that you can create <i></i>
For example, to that hello that is contained in the p, you can give it the properties you want, such as width, height, font type etc ...
Containers:
Everything is treated as if it were some box structures, which are placed next to each other, except for some labels that themselves have a display: block, which will be placed below, regardless of whether their previous box has not occupied 100% of the screen ...
To place these containers, you will have to use the class="row" and within the col-something and make the structure that best suits you, or have asked you to.
For that reason the philosophy ... of how you distribute it is yours "how much it has to occupy, etc".
If it is true that with html5, "we can divide" the content so that a developer is more readable to read.
For example, imagine a newspaper: it has the football section, the music section ... etc and inside each one more things ...
<section class="futbol">
<article="seccionEspañola">
<div> </div>
</article>
<article="seccionFrancesa">
<div> </div>
</article>
</section>