Wood lathes come in a range of sizes, but all do the same thing: they spin a securely mounted workpiece while it's being formed to the desired shape with a variety of turning skews, gouges, etc. As always, why buy when you can build? Check out these videos for some ideas:

Mini Wood Lathe by PhilipStephens007

Homemade Lathe Pt. 1 - The headstock and base by Michael Laffin

HOMEMADE LATHE (from old drill press ) by not2fast4u2c

Turning huge columns on a homemade lathe by Jesús Torres

Homemade Wood Lathe by Pilesofplenty

How To Make A Homemade Wood Lathe by bohdanmon