How To Add A Link To The Menu On Your SharePoint Site
Site owners and those who have edit permissions on a SharePoint site can customize the navigation for the site in several ways to enable the users to access the sites and pages quickly. Here we discuss how to add a link to the menu on a team site.

Background information
If the owner has customized your site, the left-hand menu or the top menu may not be there. In SharePoint team site, you can customize the left-hand menu only unless you are working in classic mode. Editing or making changes to the navigation of the site requires the owner or edit permissions. In SharePoint server 2010, you will be able to customize the top link bar for navigating the site.
Also, for those organizations that have set up targeted release options in Office 365, this will mean that you will not be able to see some features or they might look different from how they are described in help articles.
Now we discuss how to add a link to the menu on a team site.
How to add a link to the left-hand menu on a team site
On the left-hand menu, click ‘Edit’
Hover over the menu to the location where you wish to add the link and click + and the down arrow.
Choose any one of the following link options on the ‘Add a link dialogue box:
URL
Choose this option to add the link to any item located inside or outside your company. Enter the address and a name to display.
Conversations
This is meant to add a link to the group conversations on Office 365 connected to the team site. Enter a display name for the link and the address is added automatically. This cannot be edited.
Calendar
Use this option to add a link to the Office 365 group calendar connected with the team site. Just add a display name for the link to add the address automatically, which cannot be edited.
Notebook
Use this particular option for adding a link to the OneNote notebook connected to the team site. Enter a display name for the link to add the address automatically, which cannot be edited.
Planner
This link is used to add a link to the Microsoft Planner instance connected to the team site. You just have to enter a name to display for the link to add the address automatically which cannot be edited.
Once you are done with the above steps, click OK.
If you wish to add a page to the menu from the Site Pages list, select Pages from the left-hand menu and choose the page you wish to add. Then click …
Then click add to navigation
Once you are done with adding the link to the menu, click ‘Save’ or click ‘Cancel’ to discard the changes made.
Important note:
SharePoint is programmed to add recent items automatically. Therefore, it is not possible to add links to the recent menu.