If you are looking at Salesforce Setup menu, there is a sub menu under Home called Custom Links.
If you create new custom link, once done, click Save button and it will show you a message "The new custom link will not be displayed to users until you create a custom links component and then add that component to a home page layout."
What is above this message mean?
1. Go to Home Page Components in Home setup menu.
Click New button, select Type = Links, and give a name, example: Johan's Custom Link. You should see the custom link label just added, select it and click "Add" arrow button.
2. Go to Home Page Layouts in Home setup menu.
Select any layout needed, click Edit button and tick component you just added in Narrow Components to Show, then arrange the order.
3. How it will be shown in Salesforce?
Click Home tab. You should see a component of custom links.
Summary: by using Custom Links in Home within a component, you can add many useful links for your Salesforce users if the links do not need to be a tab.