Currently, you can add affiliate links to pages and post using two ways
Short code - You can copy the short code from manage affiliate links and paste it on your post or page in classic editor or Gutenberg editor, please refer to the example below.
[aa_link id=7] Will create a link with title as 'example affiliate link'
[aa_link id=7]new title[/aa_link] if content is provided in between shortcode the link title will be set to new 'new title'
Gutenberg Rich text toolbar - When you type in Gutenberg a text box editor popup appears click on the arrow button and then click on Affiliate Link which contains WPAdCenter Logo in it refer to the screenshots below
after clicking on it, a popover appears where you can select the affiliate links which you have created refer the screenshot below
popover with select box to select link
please note the cursor in above example currently it's blank which means when you apply a link to it the title would be what you have provided in affiliate link post type (refer the screenshot below). but if you have a selected a word, the link will be attached to the word itself.
newly generated affiliate link
You could also delete it using the delete button provided on the popover link will be deleted in that case not the text.