Asterisk is pretty straightforward to install if you get a distro from a myriad of sites. You have options such as getting the source code directly, which if you are a Linux geek, you can run scripts into a Linux system and then run that as a “service” or “damon” (an application that runs without a user login or is dependent on a user to run it.)
Distros are the best if you are not the most experienced. The problems you may run into is installation of unnecessary resources. In some cases distros will indicate it will install services such as GIMP, the open source Photoshop and Adobe reader compatible app, and other odd apps or services that aren’t relevant to telephony. Whether or not these apps are actually installed is another thing.
After installation, it’s best to set up the IP configuration.
Host name: asterisk-x.local
IP address: 192.168.1.97
Gateway: 192.168.1.1 (this router isn’t directly exposed to the Internet, and some newer distros will whine that it can’t connect to get updates. If it’s not exposed to the outside world, I wouldn’t bother updating immediately, just when you got the time to do it, just do it manually.)
There is another screen for the firewall, I enabled what was relevant for telephony, I use SSH to log into the system remotely, I enabled SMTP (for voicemail), TFTP and a few other ports including HTTP and HTTPS. I keep other ports off to ensure the reliability of the system.
Once this is completed, go to your computer that is tied to the same network as the Asterisk and access it (in this example http://192.168.1.97:8006.) Check your distro’s documentation as some require HTTPS and some require a “port”, that four digit number following the colon to access it.