Debian backports are according to its homepage
Backports are packages taken from the next Debian release (called "testing"), adjusted and recompiled for usage on Debian stable. Because the package is also present in the next Debian release, you can easily upgrade your stable+backports system once the next Debian release comes out. (In a few cases, usually for security updates, backports are also created from the Debian unstable distribution.)
To use these packages you need to edit sources.list file
And add this line, can be at the end
deb http://deb.debian.org/debian buster-backports main
update your tree
sudo apt update
Then you can install packages by selecting backports repositories.
sudo apt-get -t buster-backports install package
You put buster-backports after the -t, because that is the name of the repository in your sources.list, if you are running another version of Debian, change accordingly.