This is what I found on Wikipedia about huns: "The Strategikon states the Huns typically used mail, swords, bows, and lances, and that most Hunnic warriors were armed with both the bow and lance and used them interchangeably as needed." My question is: it is possible to use both bow and lance on horseback? I know that other nomadic people used them both, but not by the same person. For example the mongols had both light cavalry with bows and heavy cavalry with lances. But it seems that the huns had some sort of a mix between these two. How did the huns hang their lance while they used the bow(that is what intrigues me)?
It's a common combination. To be able to keep the lance while shooting, the lance is usually fitted with a shoulder strap, and hung over one shoulder. It could have also been hung diagonally across the back, and this is commonly shown in modern art. However, I don't recall seeing this in contemporary art (if a reader known of such art, please post a link!). To keep the lance more stable while riding, the butt is often placed in a leather "bucket" near the stirrup (often attached to the stirrup) or secured to the stirrup with a strap.
https://i.pinimg.com/474x/f9/ef/b4/f9efb4b3f8a5abf13274ebdf98f7eee3--napoleonic-wars-warriors.jpg
https://myarmoury.com/talk/files/orlowski_bashkirs_601.jpg (the lancer isn't visibly carrying a bow (or gun), but the shoulder strap and stirrup strap are clearly shown)
Late 19th century British lances (with strap) and lance buckets: http://www.uniformology.com/LANCERS-11.html (for use with rifles rather than bows)
The combination of lance and bow, with not straps visible on the lance, is common in art:
https://en.wikipedia.org/wiki/File:Taq-e_Bostan_-_equestrian_statue.jpg
https://en.wikipedia.org/wiki/File:Ardachir_relief_Firuzabad_1.jpg
https://en.wikipedia.org/wiki/File:Tabriz_Sasanian_Plate_2.jpg
For these, it's probably just the case that the artist didn't show the straps. It's possible that the lance was just dropped if the bow was to be used, but in general, it is good practice to keep the lance available.
We also see a similar combination of lance and carbine/rifle/musket:
Due to the difficulty of reloading long muzzle-loading firearms on horseback, the combination of musket/arquebus, bow, and lance is also common:
