I installed most software from the terminal. I saw that with some programs people give commands like this for example:
sudo apt-add-repository ppa:jfi/ppa
sudo apt-get update
sudo apt-get install psensor
But some just give commands like this:
sudo apt-get install psensor
If that is the case, and I want to add repository (so that program receives updates more quickly, if I understood it right), how do I know what comes after ppa:? How can I find that out?
From Launchpad:
Personal Package Archives (PPA) allow users to upload Ubuntu source packages to be built and published as an apt repository by Launchpad
Launchpad is a website developed and maintained by creators of Ubuntu that allows users to develop and maintain open-source software.
If you have found a nice PPA and you want to add it to your repository, this is the general format:
sudo add-apt-repository ppa:user/ppa-name
Every PPA has its own page in Lanuchpad website. For example, the one mentioned in your post has its page here: https://launchpad.net/~jfi/+archive/ubuntu/ppa
If you look at the PPA's overview page, under the heading Adding this PPA to your system, you can see the location of PPA. See the below image:
You can use the location to replace ppa:user/ppa-name in the above command. So, in your case it is:
sudo add-apt-repository ppa:jfi/ppa
To know more about PPA's you can read them in What are PPAs and how do I use them?
If you want to find out the PPA of a repository, you can find them in launchpad
