There are few Page Builder Concepts you need to understand to use the Page Builder effectively
A section is the base building block, think of a section like a group of elements in a page. A section will have 1 or more rows.
As the name suggests a row will hold exactly one row of elements, a row can contain columns, gallery or an image slider
A column contains 1 or more modules, the column width depends on the column layout selected
A module is what represents your content. A Text Module will let you insert Text, while an image module lets you insert an image and so on