Just a quick tip in case you’re not using a major desktop environment like KDE. I’m using LXQT at the moment and as a screensaver it uses xscreensaver. It has no default shortcut to lock the screen, so I looked around a little bit and I found this command:
xscreensaver-command -lock
which will fire up the screensaver locking the screen.
to set it up just open the lxqt settings and add a new global shortcut (mine is Win + L) and save. That’s it, now everytime you need to lock your screen just hit the shortcut and voilà..