Use tabs for web pages in Safari on Mac
When you’re surfing the web or researching a subject, avoid cluttering your desktop with multiple windows. You can instead view multiple web pages in a single Safari window by using tabs.
Preview a tab
In the Safari app
on your Mac, move the pointer over a tab.
Open a new tab
In the Safari app
on your Mac, click the New Tab button 
in the toolbar.To change the webpage that opens in new tabs, choose Safari > Settings, click General, click the New tabs open with pop-up menu, then choose an option. See Change General settings.
Open a webpage or PDF in a new tab
In the Safari app on your Mac, do any of the following:
Command-click a link on a webpage or a Favourites icon.
Command-click the Back button
or Forward button 
to open the previous or next webpage in a new tab.Type in the Smart Search field, then Command-click an item in the search suggestions, or press Command-Return.
Tip: To use these Command-key shortcuts to open webpages in new windows instead of new tabs, choose Safari > Settings, click Tabs, then deselect ⌘-click opens a link in a new tab. See Change Tabs settings.
Open a webpage in a new tab from the bookmarks sidebar
In the Safari app on your Mac, do any of the following:
Control-click a bookmark, then choose Open in New Tab from the shortcut menu.
Control-click a bookmarks folder, then choose Open in New Tabs.
Each bookmark in the folder opens in a new tab.
To open the bookmarks sidebar, click the Sidebar button 
in the toolbar, then click Bookmarks.
Open a tab in another window
In the Safari app
on your Mac, drag the tab over the desktop or choose Window > Move Tab to New Window.You can also drag the tab of one Safari window to the tab bar of another.
Note: Tabs in private windows can only be moved to other private windows. Tabs in non-private windows can only be moved to other non-private windows.
Automatically open webpages in tabs
In the Safari app
on your Mac, choose Safari > Settings, then click Tabs.Click the “Open pages in tabs instead of windows” pop-up menu, then choose an option:
Never: Links designed to open in new windows open in new windows.
Automatically: Links designed to open in new windows open in new tabs.
Always: All links designed to open in new windows open in new tabs, including links designed to open in specially formatted separate windows.
Reopen a recently closed tab
In the Safari app
on your Mac, choose History > Recently Closed, then choose the web page you want to reopen.You can also reopen a closed tab or window.