Panning is positioning the different tracks in a musical arrangement at different points between the left & right speakers or headphones. It could take you 5 minutes to to simply pan all the tracks in a small arrangement with only a few tracks, but usually it would be a larger part of a more complex mix of a song with many tracks, where you creatively devise a well-balanced stereo image with a combination of simple panning, doubling, and the use of stereo effects. The processing that's applied in a mix may change depending on how the tracks are arranged in the stereo image, and the decisions that go into determining the panned locations of the various tracks may be informed by the way the musical parts blend as the mix is gradually built up.
To me, panning is an integral part of mixing, but mixing can be a complex process that involves many different aspects, including static & dynamic level adjustments, technical processing, creative processing, and stereo imaging [panning]. It seems to me that focusing on the idea of panning as some kind of isolated thing to do misses the point of that..
You could mix a song while monitoring [listening] on anything, but if you plan to distribute it to the public in any way, and want it to sound like a professional production -- including for those who may listen to it on proper speakers & headphones -- then you'd really need a proper listening environment when mixing. However, if you're not really concerned about that, or if you're not ready for [or interested in] building up mixing skills at this point [which would take time and practice], then I guess you could hire someone to mix the tracks -- obviously many people do that, that's why those mixing services are available. It's all up to you -- I don't know what your musical arrangements will be like, whether you plan to distribute them to the public, or how important it is to you to have professional-sounding mixes, so I can't tell you what to do..