While you are writing the text highlight the portion of a word you want to link to and then click the link field above. It will bring up a drag down list of your hubs. If you have already written the hub, then simply edit the hub from your account page, edit the text field where you want the link, and then add them.
If you want your links to continue at the bottom of your hub then you have to group your Hubs into
You can also add a link field in your hubs. To add links to the link field take a link from one of your hub pages and add it in the box and click "add".
If you want your links to continue at the bottom of your page, then you can go to the your hubs page and make groups for them. Grouping them this way will allow the continuation.