To connect to A2SERVER from your Apple II:
(An alternative to the below is to boot your Apple II over the network -- check that out too.)
Start up A2SERVER and wait (potentially up to a minute) until you get to the login prompt. You do not need to log in. On a Raspberry Pi, you can see that it's ready when the the normally irregular ACT or OK LED blinks steadily and rapidly for ten seconds.
If you are on a IIe, boot from the Workstation Card disk, and choose "Log On".
If you are on a IIgs, open the AppleShare control panel. If you don't have it, use the GS/OS installer disks to custom install the script called "Network: AppleShare" to your startup disk. If you are on a floppy-only system, you can instead use the script "Network: AppleShare, 3.5" disk" to make a bootable disk, or consider setting up network boot.
There is also an obsolete IIgs Workstation Disk (see link below) that boots into ProDOS 16 rather than GS/OS, and has the same ProDOS 8 applications for server access as the IIe disk. You probably don't want to use it.
"a2server" or "raspberrypi" should appear in the list of server names. Log in as Guest, and select the A2FILES volume if prompted.. (You can also log in as a registered user, but it's exactly the same.)
The network volumes hosted by A2SERVER will appear on the Finder desktop in GS/OS; in ProDOS 8, you can type
IIe Workstation Card, 800K: raw image ShrinkIt image
IIe Workstation Card, Logon/Logoff/BASIC only, 140K: raw image ShrinkIt image
IIe Workstation Card, System Utilities/BASIC only, 140K: raw image ShrinkIt image
IIgs Workstation, 800K [superseded by GS/OS AppleShare software]: raw image ShrinkIt image
A2SERVER home page