For a full description of Winlink, look it up at https://winlink.org/ (See the "What is Winlink" video at the bottom of the winlink.org page.) Here is a "Cliff Notes" version for our use.
Winlink is a world-wide system for transferring email via radio that links RF to the internet through HF and VHF gateways called "Radio Message Servers" (RMS). All these RMS's are connected to each other via the internet.
A VHF RMS uses AX.25 packet. An HF RMS is most likely to use a "sound card" mode called Winmor, which is generated by the standard Winlink client known as Winlink Express (older versions were called RMS Express.) A few HF gateways use "PACTOR", which requires a dedicated, proprietary termincal node controller (TNC). There is a school of thought that says PACTOR is much more reliable at getting messages through than Winmor. Unfortunately, PACTOR TNC's are very, very expensive, so Winmor is likely to be used by hams.
As Winlink users install WInlink Express, they register with the Winlink system and receive a Winlink address, i.e. email@example.com This is how messages are routed in the system.
Illinois ARES is developing a system of Winlink Gateways on 2 meters on 145.610 MHz. Gateways in the area include K9EW-10 in Westmont, NE9MA-10 in Naperville, WX9CTA in Sugar Grove, and N9EF-10 in Sandwich. All are simplex packet on 1200 Baud. The goal of this system is to be able to feed email via the internet to addresses and to Winlink-equipped stations statewide and beyond.
A map of Winlink VHF Gateways is at: https://winlink.org/RMSChannels
In the bar at the top of the map, select "Packet" to see the VHF RMS gateways.
Winlink can also be used in a peer-to-peer setup.
So, for now, the primary function of Winlink - either VHF or HF - is to be able to send email through a gateway to an addressee on the internet or to another Winlink station. This really needs to be tested in a multiple station, net-like exercise. This may change, or the author may be overlooking something.
On VHF, Winlink requires (obviously) a suitable transceiver and a computer. You then need a device or software that handles 1200 baud AX.25 packet to connect the two. Finally, you need to download Winlink client software - specifically Winlink Express, which has replaced an earlier client "RMS Express."
Winlink Express can be downloaded from https://www.winlink.org/ You'll see "Get Winlink Express" on the right-hand side of the page.
Installation is very straightforward, but you will have to register with the Winlink program to get a Winlink address. (You don't have to donate money to do so unless you want to.) I also recommend that you un-install any versions of RMS Express you might have on your computer before installing "Winlink Express". For some reason, on my computer, the icon still shows "RMS Express", but the program works fine
Traditionally, hams used stand-alone TNC's - Kantronics, MFJ's, etc. for packet. If you have one lying around from your days of playing with packet mailboxes, or can glom onto one, that will work.
A recently developed program called "Soundmodem" allows Winlink to handle packet using a sound-card device. This enables you to need only one "accessory", such as a Signalink or Rigblaster to handle the sound card modes AND Winlink packet. Instructions will be posted later. For info on Soundmodem, see: http://uz7.ho.ua/packetradio.htm Several area hams have successfully installed and are using "Soundmodem".
Winlink Express also offers templates to a wide range of forms - ARRL, ICS, and on and on. This can be really helpful