I’m assuming you want a spherical panorama.
Insert a spherical camera,
rotate it 90 degrees on the X-axis so it’s facing along the ground plane,
move it above the ground if necessary,
set your aspect ratio in the render room (usually about 2 x 1, try to get as high a resolution as you can if you’re using it as a background),
select the spherical camera on the output tab,
and hit render.
Of course it helps to have a 360 degree scene to render.