There's one concept/design pattern you should know - in the Visual Composer editor mode you'll have "Add element" button, which you should click or drag to the working canvas, to add content block or row to your page. If you are adding row element to your page pay attention that it will automatically add column element within row. You can later add more columns within row and change their behaviour. Read more about rows and columns in Elements section.
Clicking the "Add element" button will show the content element selection menu. Content blocks are divided into categories (Show all, Content, Social, Structure, WordPress Widgets, etc.).