If you learned Elementor with sections, inner sections and columns, containers will feel unfamiliar for about twenty minutes and then feel obviously better. A container is a flexbox element: it holds children, and you decide whether those children stack or sit side by side.
Direction is the main control
Every container is either horizontal or vertical. A vertical container stacks its children, which is what you want for a page wrapper. A horizontal container places them in a row, which is what you want for a feature grid. Nesting a horizontal container inside a vertical one replaces what used to need a section plus an inner section.
Building a hero
Start with a vertical container, set the content width, and drop in a heading, a paragraph and a button. Use the gap setting instead of adding margins to each widget. Gaps are one value in one place, so changing the rhythm of the page is one edit rather than five.
A three-column row
Add a horizontal container and put three vertical containers inside it. Each one holds an icon, a heading and some text. Set the outer container to wrap so the three columns become a single stack on mobile without any custom CSS.
Why this is worth relearning
Containers output far less markup than the old column structure, which means faster pages. They also respond to alignment settings the way CSS actually works, so vertical centering stops being a fight.