To take a screenshot on Samsung Galaxy S8 device, you have to press the Power + Volume Down buttons to do that. This probably makes switching from most Android devices easier, but someone transitioning from the S7 (or earlier) might be a bit confused.
If pressing physical buttons is too much work, you can always hold down on the home button to open Google Assistant, and press the ‘Share Screenshot‘ button. The S8 also allows you to take a screenshot by swiping the edge of your hand across the screen (while still keeping it on the screen). Plenty of options for your screenshot-taking needs.
Once you actually capture it, the S8 has a neat feature you can use called Scroll capture. Like several browser extensions, this scrolls down whatever content you are viewing and adds more to the screenshot.