The paragraph is the basic block. Paragraph Block – Documentation – WordPress.org

A new paragraph block is created if you tab or press return in the title field. Once you are working in a paragraph block a new one is created if you press return.

When you are working in a paragraph block the Floating Block toolbar will appear if you move the mouse. Hovering over the controls will tell you what they do. You can set the floating toolbar to stick to the top of the screen. I prefer this option especially on a tablet.