Sometimes there might come a situation where Debian stable is just too old. This is usually related to hardware support of some component that the computer has that has no current support on a kernel that Debian stable ships with. Kernel is a typical example but others may exist as well. Backports might be of help when trying to get some more support to hardware. However, before proceeding it is good to notice that backports might cause issues down the line if used too carelessly.
A typical case of an issue might be that when the next Debian stable eventually arrives upgrade might be tricky if you have some packages that are more recent than those Debian is offering. This used to be more of a big deal back in the day. Currently, I believe that backports generally do not provide any significant risk that could not be handled during upgrades. Caution is still adivised,
To add backports to Debian stable you need to do the add the following entry (as sudo or root) to your /etc/apt/sources.list or equivalent file under /etc/apt/sources.list.d folder structure:
deb http://deb.debian.org/debian bullseye-backports main contrib non-free
After the above line is added do: sudo apt-get update
Installing from backports is done by first locating the package you want to install. A good source for this is https://backports.debian.org/
When the package of choice is found, then the installation command will be, for example:
sudo apt install linux-image-amd64/bullseye-backports
On the above command, linux-image-amd64 is a metapackage that will install a more later kernel from Debian backports. Finally, to start using the later kernel, I would need to reboot my computer.