Basically Digital communications is based in to connect your Transceiver to your PC for to send Data (files, comments, photos, etc.) to other Stations. You can send photos (SSTV), do a chat (packet, RTTY...), send and receive files, do DX, digital CW, etc. Finally to do Contacts by radio, but in a diferent Way.
You can practise this with equipment you have now, your transceiver and your PC. Is necessary only a small interface to join they, as for example a modem for radio, a TNC or simply your PC Sound Card (for last one is necesary a simple home made wire with PTT conmutator).
I use a Core i3 PC 3000 Mhz. with a Modem SB-1000 USB by CG Antenna but I still have my old Modem Sitelco PRS 1.200 K that worked under Windows 98, two TNC inside my Kenwood equipments and a home made adaptor for mi sound card. Besides you can use every kind of machines, I started using and old 386 with 2Mb of Ram on MS-Dos and windows 3.1, But is clear that if you use better PC you would obtain better results and nowadays there are a lot of very good programs.
My favourite software for Windows is AGW Packet Engine with Winpack (for packet) and Ui-View (for APRS) which give me really good results, also I use HRD for CAT and Digital modes.
See here my last position mobile received via APRS mode or write another call sign in the box:
To learn more about Digital modes Click here.