Taking one-handed pictures with your phone can quickly devolve into a juggling act. You have to secure the phone in landscape mode (if you're doing it right), tap to focus, and then somehow hit the shutter button without shaking the device too much. Fortunately, Samsung has a nifty feature that'll help you keep a more secure grip on your Galaxy S9 or S9+ as you take photos with one hand.
The Galaxy S9 has an extra capture button that you can enable and place anywhere on the screen to make snapping photos a lot more convenient. The option is buried deep within the camera's settings, but it's very simple to set up once you find it. With this feature on, you can take photos with minimal finger movement and minimize the risk of dropping your phone in the process.
To enable the floating shutter button on your S9's camera, open the Camera app and tap on cog-shaped settings button. Once inside the settings page, scroll down to the bottom half of the screen and tap on "Floating Camera Button" near the bottom of the screen. Exit settings once it's toggled on, and you'll now have an extra button that you can freely move around to better suit your needs.
For those moments where the floating button becomes too intrusive no matter where you put it, you can instantly remove it by doing a long-press on the button. A tiny button with a minus sign will appear next to the floating button, so tap on it to delete the extra button.