How does this generally work?
Are logon scripts used? If yes, is there a standard script to trigger installation of softwares when a client logs on? (an example could really help)
Or is another method used?
Installing software remotely to computers on a domain is best done using group policy.
Beware of using group policy. If you expect to have lots of sites or lots of OU's, using GPO will become real painful, real fast.
I'd recommend an actual software distribution tool such as MS SCCM for software, and limiting Group Policy to what it's good at -- settings, user rights, etc.