Dell Optiplex 3060
Add the backports repository:
echo deb http://http.debian.net/debian stretch-backports main contrib non-free > /etc/apt/sources.list.d/stretch-backports.list (Yes, we’re adding contrib and non-free, they’ll come in handy later...)
Install the backported kernel:
apt update apt -t stretch-backports install linux-image-amd64
This won’t replace your current kernel, so you can always boot that instead if things go wrong.
The second is firmware. Most GPUs, and many wi-fi adapters, need firmware, which might not be installed by default (because source code is generally not available, so it’s not made available as part of Debian, but instead in the non-free repositories). To install the available firmware, from backports too (might as well):
apt install -t stretch-backports firmware-linux