See the web pages open on your other devices in Safari on Mac
The Tab Overview button 
lets you view the web pages you have open on your iPhone or iPod touch (iOS 11 or later), iPad, and your other Mac computers (macOS Sierra or later). Make sure Safari is turned on in iCloud preferences (on your Mac) and in Settings > [your name] > iCloud (on your iPhone, iPad and iPod touch).
View a web page open on another device
In the Safari app
on your Mac, click the Tab Overview button .You can see the web pages open on your Mac along with lists of the web pages open on your other devices.
Click a web page to open it.
Tip: You can also enter part of the page’s name in the Smart Search field, then click the page in the iCloud Tabs section of your search results.
Close a web page open on another device
In the Safari app
on your Mac, click the Tab Overview button .Move the pointer over a web page listed below your device, then click the Close button
that appears to the right.
Hand off a web page between devices
When your iPhone, iPad or iPod touch is near your Mac, click or swipe the Handoff icon near the end of the Dock (on your Mac), on the Lock Screen (on your iPhone, iPad or iPod touch with a Home button) or in the multitasking view (on your iPhone X or later, or iPad Pro). The web page you’re viewing on one device is handed off to the other. See Pick up where you left off with Handoff.
You can’t use Handoff to pass private windows.