If the input or output is plain text, copying and pasting should work as expected.
Unfortunately, if the input or output is 2D Math, then copying and pasting likely won't work. This is because, currently, the content on the webpage, which is not directly produced by Maple, is not in a Maple-readable format.
The best option is to download the help page using the Download Help Document button at the end of the page (see below), then open and execute the resulting Maple file.
Alternatively, you can access the help page from within Maple, then open it as a worksheet so that you can execute it as is: