Ah, hello. I was going to respond on another thread of yours (and welcome you to the game, while I was at it), but someone pointed you at the wiki before I got chance to say anything any more useful.
There are several walk-throughs linked there which might help with a lot of your questions, so if you've not lost the general URL for that, already, I'd check that out.
But the specific answer to your question is to use the "b" key, then you get a menu ("c" for constructions, such as walls, "w" for various workshops, other letters for other things, it's all written down on the screen, but you may have to wander in and out of various sub-menus when you're still learning how it's organised) and then you get to choose which particular materials you have at hand that want to make them out of. Which, as long as you're not too fussy and
have mined out some rock/cut down some trees already, is probably the first item on the list. (It will tell you if there are no materials available, or there's some other issue like the site being blocked by something like a tree. You may also need things like buckets, barrels and anvils for various workshops, but the principle is the same once you
have them.)
Later on, you may decide to make sure you don't use your wood or certain types of rock for a given workshop, because you want to use that type of material for something else (or for use within this or another workshop), but you'll sort out all your own preferences for that sort of thing as you play the game over and over and over, making mistakes and deciding whether you're going to play according to any particular aesthetic or practical policies.
Really, though, the main page of the wiki has (IIRC) a whole box-out containing links to its pages that are specifically guides for starting out, and they'll answer this type of question better than I know I can.
Not that you
can't ask here, but I think you'll move more quickly between one puzzling issue and another if you try the guides. And probably find answers to questions you didn't even know you might have had to ask. And we can always help try clarify anything that's unclear, or inexplicably not even covered.
Anyway, again, nice to see you. I also spotted you in the Suggestions thread, which shows enthusiasm that I admire (albeit that you probably need to first check to make sure that what you're suggesting isn't an oft-mentioned thing
). I'm sure that playing the game will be interesting, and don't be afraid of making mistakes, because by the next fort or twenty you'll have worked out how not to make those mistakes (and be making some others, from which you'll also learn). Remember: Losing is fun!!!