OP: I definitely concur with the recommendation above that you give the late Sheldon Brown's website some study if you're really a "newbie" to C&V bicycles. Though simple in design, due to multiple, often incompatible variants classic threaded headsets are a fairly complex subject with many ways to get in trouble if you don't do your homework.
Threaded headsets require either special adapters (which allow use of a newer threadless stem) or quill stems (older design and intended to be used with threaded headsets). Headsets also interface with both frame and fork, so all four parts (quill stem or adapter, frame, fork, and headset) must be compatible. And due to variations within different designs of theoretically compatible headset/frame/fork/stem combinations, sometimes such theoretically compatible combinations . . . . aren't. One example: a standard ISO 1" headset with a large stack height might not be usable with a theoretically compatible frame and fork if the fork has previously been used with a shorter headset and cut to fit that configuration exactly.
As you might have guessed, quill stems are also an area with multiple, sometimes incompatible variants and ways to get in trouble. Ditto for C&V frames and forks.
These three URLs give a decent overview of the variations among headsets and stems.
https://www.sheldonbrown.com/cribsheet-headsets.html
https://www.sheldonbrown.com/cribsheet-handlebars.html
https://www.sheldonbrown.com/headsets.html
Best of luck, and welcome.