On a baloon, the wind is the GPS-derived ground speed. There is nothing else to do.
In a powered aircraft, calculating the wind requires
- GS (from GPS)
- track (from GPS)
- TAS (which requires IAS, altitude, and temperature)
- heading (from fluxgate magnetometer compass, etc)
A G296 cannot calculate the wind because has only the first 2. There is an E6B calculator in there into which you can enter the other 2 values manually. Most aviation GPSs have such a function. Most of the panel mounted IFR units can get the extra data supplied from an air data computer so you don't need to fill them in manually.