The Get Elevation command fills in elevation data for hand-drawn tracks or GPS tracklogs with missing elevation data. For each point on the track that doesn't have elevation data, the Get Elevation command retrieves the best known elevation data for that location. Elevation data comes from a variety of sources, including the National Elevation Dataset (USGS NED) for points in the United States, and from NASA's Shuttle Radar Topography Mission (NASA SRTM).
A progress bar at the bottom of the main ExpertGPS window will help you monitor the retrieval of elevation data. If the command fails, select the track and try the command again.