Heh, blacksmithing is very costly and time-consuming (you either have to buy or mine the ingots/ores somehow~.)
A manual has 30 uses. Each use completes a certain % of an item. The ammount completed depends on the item.
For details for each item, see this:
Blacksmith List - Mabinogi World Wiki
The success rate you'll have for each item is dependent on your skill rank and on the rank of the item you're making. I think you
can make armor...even if you're rank F. But you're success rate will be....bad.
Let's look at Male Valencia, rank 5. Using the table at the bottom of the page, and assuming a skill rank of F, you'll have a 1% chance of success. Good luck.
But yeah, most people don't try making armor until a decent rank, because it's pretty expensive and it's a waste of money. But getting to that decent rank is difficult in itself.