Highlight your link text in your page or post while editing it, click the link icon (looks like a chain link) and enter the url you want to link to. Save and that's it!

You can use the link icon in your editor to paste the link in and make some text clickable. You can also edit one of the images in your post and make it a link. If the link you’re trying to place is an amazon image or image + text link, you can simply paste the code on your text tab or code editor page where you want the link to appear.

If its an actual Affiliate Link then you have an article in Edit Mode in your Wordpress.

Then you highlight a piece of relevant text.
Then you click on the Paperclip icon in the menu.
A box will appear directly underneath the highlighted text.
You insert your Affiliate Link.
Then you click on the little Cog Wheel to the right of the Box.
Next small screen - make sure your link is showing in the box and tick the Open In New Tab box.
Then you click on Insert.

The highlighted text should have changed to blue.
Save article and click on Preview to test the link.
If it takes you to where its supposed to then job done.

You can also insert your link into an image.

Hope alls clear now.

if you go to your dashboard when writing an article there is a symbol on your toolbar

If you highlight the word you want to link then press that symbol circled in red then the box will appear.

This is where you enter the URL link and then press the blue enter button.

regards
Darren