I recently had to put my Windows machine in the shop, so I fired up an old Macbook a friend gave me.
I have a bunch of graphs I was going to post over on serverfault. They're presently in a webpage. Normally, I'd right-click, copy, launch irfanview, paste, highlight the area I want, then save the selected area, or copy it to the clipboard and paste it into mspaint. If I wanted to draw attention to an area, I'd hit F12, and doodle on it.
It might not be intuitive, but it's what I'm used to after years of Windows.
To be clear, these are large graphs, and I want to highlight the areas of interest, and produce a single image which illustrates the problem.
There's a whole ecosystem in the Mac world I'm unfamiliar with. What's the Mac way to do this? I don't want to take my Windows (and Linux) prejudices into the Mac world. Especially for editing graphics.