There are several ways of linking to other pages or documents - here are some examples. See the Confluence Display files and images page and the Confluence Links page for further details.
A link to another wiki page
A link to another wiki page
A link to a web page
Simply highlight the text you want to link, then select Insert link then Web link, and type or paste in the URL of the linked web page.
Thumbnail or attachment?
Insert a pdf document as a thumbnail
or as an attachment:
Insert a pdf document as a link
Links to Google documents
You can link to Google folders, Google Docs, Google Sheets, Google Forms and more.