another hubber Mr. GA Anderson has a great hub on "how to links". There is a question of relevance for the reader when leaving links. Does the link lead to related material, if so ok, if not, think twice.
If you have related hubs put them in groups and then use the RSS feed capsule which will list a maximum of eight hubs per group.
Both the learning centre and Mr. Anderson explain the use of this very well.
In any "Text" capsule there are two symbols of chain links, one full and one broken. The use of this couldn't be simpler. It is better to open to HP tabs, the one you are editing and the one you want to link to.
In the text capsule of the one you are editing highlight the words you want to use for the link and click the full chain link. The box that opens allows for you to enter a title and a URL. Go to the other tab, the hub you want to link to, copy the URL, return and paste in the box of the hub you are editing and click done or save. The highlighted text will turn blue indicating that it is a link,