Elementor is a page builder plugin. On any content it is enabled for, it replaces the standard editor with a canvas where you drag widgets into place and style them in a side panel, seeing the result immediately.
Free and Pro
The free version covers layout and the common content widgets, which is enough for most brochure sites. Pro adds the theme builder, which is how you design headers, footers, single templates and archive templates, plus dynamic content and form widgets.
The trade-off
Builders trade page weight for speed of building. Containers made the output considerably leaner than the old column system, but a builder page still carries more CSS than a hand-coded one. For most sites that trade is worth it; for a very large content site it is worth measuring.