Before using Universal Clipboard, you must sign in to iCloud (using the same account) on each device.
On macOS, you can sign in by opening System Preferences > Internet Accounts > iCloud.
On iOS, you can sign in by going to Settings > Sign in to your iPhone.
On macOS, you can enable both bluetooth and WiFi by clicking on the respective icons in the status menu.
On iOS, you can enable both in Settings. Click on the Settings app icon, then look for Wi-Fi and Bluetooth. Click into each and toggle the service on. Alternatively, each service can be enabled from the Control Center. To open the Control Center, swipe down from the top right (or up from the bottom on older devices).
To enable Handoff on macOS, go to System Preferences > General, then check Allow Handoff between this Mac and your iCloud devices.
On iOS, go to Settings > General > AirPlay & Handoff, then toggle on Handoff.
With handoff enabled on multiple devices, you can now use the Universal Clipboard. To do so, simply copy text, images, or video on one device and paste on the other. See the following instructions for more details.
Copy on Mac, Paste on iPhone
To copy in Mac, you must highlight (if text) then right click. Then select Copy. Alternatively, highlight or select what you want to copy, then type CMD + c (at the same time).
To paste on iPhone, press down on an input field until a menu appears. You should see an option to Paste. Also, some apps will allow you to insert text, images, and videos from your clipboard.
Copy on iPhone, Paste on Mac
To copy on an iPhone, hold down on the object you want to copy. If text, you'll be presented with highlight bars. Simply drag the bars to highlight the text you want to copy. Alongside the highlight bars, you'll see a menu with an option to Copy. Click it when ready.
To paste on Mac, you can right click on an input field (or anything that accepts input) and select Paste. Or, you can select the field with your cursor and type CMD + v (at the same time).