Click on Node overview in the Content menu.
Before adding a new node, decide if this node will be at the root level, or a sub-node of an existing other node.
When adding a node at the root level, click on the + New button.
When adding a node as a sub-page, click on the + button next to the parent node.
Choose a node-type and enter all node content. If all required fields are filled out, the node will be saved automatically.