Html treat every element in it as a box. Abox has a height, width. As same html element has also a height and width. This approach is called as "Box-Model".

Both have there own benefit. Bootstrap offer "Ready-Mate" component libraray to make it easy front-end design using that component. It gives less customisation opportunity. Other side Tailwind also have component library but most of them are premium but it has more customisation scope and used for modern age design flexiblities.

As a begainer, every "Baby-Developer has this conflict of concept like What the heck is this flex and grid? Flex is a one dimentional array which can handel lay-out either row or column. On the other side, grid is two dimensional array can handel content both row and column wise. it give us more flexiblities then flex😀

In previous HTML-4, there are something called div and table. Which are "Non-Identical to developers. For This reason it was very hard to maintain all markup and debugig. semantic tags are well known by name like: header
footer
main
section
article
aside etc.