While writing a new post, page etc, many times you need to link and reference to an old article of your website. In general, most WordPress bloggers follow the long route of linking internal content. First they search for the post, copy its URL and then mention it. The easy way of doing same thing is built-in WordPress feature which works right inside your post edit screen.
Step-1 From your Add New/Edit post page select the text then click ‘Insert Link‘ icon present in visual editor toolbar.
Step-2 Now click that small greyish dropdown link with title ‘Or link to existing content‘ present at the bottom of the box.
Step-3 Start typing the words used in the title of the post you are searching for. Find the link, click to select it and then click the ‘Add Link‘ button. That’s all.