These guidelines are current as of Archicad 17-18.
Archicad 16 was the last version to be shipped on physical media by default. Archicad 18 is distributed via download, though they might send you a DVD if you ask nicely. You don't need that.
You can install Archicad from a physical disc (16 and earlier) or you can use the disk image on the server. We keep copies of Archicad installers going back, well, back far enough that not all of them will run on our current platforms. They are located at 3 Resources/AC/AC Program Files/[versionNumber].
(A word on disk images because they are still weird after all these years. A disk image (extension: .dmg, often called a dmg) is file which, when opened, mounts a volume in the local filesystem just as if you had inserted a physical disk. It will appear in the Finder sidebar, and will probably open a window. Some applications are drag-installable, and to install the application you just drag it from that window to your Applications folder. Sometimes they even provide an alias to your Applications folder to make the process clearer. Once you have installed the application, you can/should eject the imaginary disk.)
Archicad is not drag-installable, so you need to run the installer. Whether you use a dmg or a DVD, when the window opens you will see an icon named "Archicad Installer". Run that. (Mercifully, after AC16 they got rid of the flashy installer application. They also simplified the package so there are no separate installers for CodeMeter and the like.)
Archicad doesn't use the standard package installer. It uses a custom installer written in Java. Mac OS X currently ships without Java installed. Even so, you might/probably have Java installed because it's required for other things. If not, the system will prompt you to install it, which is pretty automatic and takes a couple minutes. Then the installer will launch.
Follow the directions. Know what kind of key you have: Wibus are green plastic, CodeMeters are metal. I don't customize the installation. Use the default location, /Applications/Graphisoft. I don't import Work Environment settings; as far as I can tell this has never worked properly. (Maybe it works now. Fool me 4-6 times, shame on me.) Yes on the Dock icon, no on the Desktop icon, yes on checking for updates.
New version installations usually require a restart, because the Wibu/CodeMeter software gets in there pretty deep. I ignore the warning about closing all other programs at the beginning, but I guess I have to eventually in order to restart. If you need to apply hotfixes to the version you are installing, you can do so immediately without restarting first or even running the original version. Run the main installer, run the most recent hotfix, then restart just once.
After restart, there are a couple things that are beyond the scope of the installer.
Work Environment
Our Work Environment is heavily modified, and to me the default Archicad environment is profoundly disorienting and I can't do anything with it at all. So right after the first launch I import the work environment. The work environment is stored in the preferences, so if you are re-installing a version you have used in the past, the work environment might be OK at first launch.
DXF-DWG Translators
We don't do a lot of heavy DWG translation. Mostly we send out background plans and place consultants' DWGs as drawings to use as trace references. But that's enough to need standard translators.
The translators are located at ~ /Library/Application Support/Graphisoft/DXF-DWG Translators [versionNumber] USA/. Copies of our standard translators are on the server at 3 Resources/AC/DWG Translators/. With many things like this, you could just copy the files to that local Application Support folder, and the translators should show up in the Translation Settings. But it doesn't work.
You must go to DXF-DWG Translation Setup. (Either on the File Special menu, or, actually I usually use the Options in a DWG Publisher set.) Then Browse for the files at the server location. Set the default Import and Export translators, and update your Publisher settings as needed.
DisableCrossPlatformMountingFeatures
If you ever take solo projects away from your usual network, and have external resources (libraries, modules, drawings) on a server, you need to know about dcpmf, to (help?) prevent Archicad from spending ten minutes wailing into the abyss about the mysteriously vanished IP address ZOMG.
Archicad Updates (Hotfixes)
Since you wisely opted to let Archicad check for updates during installation, it will do just that periodically (weekly, or change it in Work Environment), and eventually you will be notified upon launching that an update is available. It could be for the application or the Archicad library or both. Go ahead and do it; they usually fix more things than they break. The updates, known as Hotfixes and identified by a sequential number like 6 and a build number like 5019, will wind up in your downloads folder. The files are disk images once again, and the update process is very similar to the original installation. It knows what to update and usually doesn't require a restart.
If you are installing a version that has had several hotfix updates, you only need to install the most recent one; it includes all the previous fixes.
The only caveat for updating immediately is if you are working in Teamwork. In that case, all users in a project have to update together, along with the BIM Server application which is running the project.