You will want to start by going to the FreeNAS website to install it at https://www.freenas.org
Once you have gone to the website you will see a big download button, click that and it will take you to another page. You can choose to fill out the information or you can just click “No thank you” at the bottom. You will want to download the most stable version which the one I am downloading is (11.2). Give it time to install, this will give you an ISO. FreeNAS can be installed on a flashdrive and I recommend this route. I also recommend having multiple flashdrives because flashdrives die so its nice to have backups. I am using the short flashdrives from SanDisk because the risk of hitting, bumping, and breaking is a lot less when its short.
You can install FreeNAS on old machines which would be a great starter for you but it will at least need 8gb of ram and then you can add more drives in for storage. Once you have FreeNAS on your flashdrive then boot off it on your machine. Hit 1 to enter the installer for it, which it will take a minute to process. You are going to choose 1 again to install. You will then select the drives you want to install it on, you will have either just the 1 or the other flashdrives you got. Use spacebar to select and then down arrow to ok. It will give you a warning that it is wiping clean your flashdrive so make sure you are not using one with content on it. Then you will give a password and click ok. The next option will be UEFI or BIOS, in this case I am selecting BIOS. When this start it will take a few minutes to start. Once it succeeds then click select ok and reboot the system.
You will find your IP for the FreeNAS at the bottom. Enter that in the browser and then it will ask for a username and password. Username will be “root” and then the password will be whatever you decided on.
What is FreeNAS?
FreeNAS is a free and open-source network-attached storage software based on FreeBSD and the OpenZFS file system.
If you want to skip all these steps, you can buy FreeNAS machines from amazon with it already on there.