If I roll up a human or kinfolk in Old World of Darkness and I am embraced by a vampire, what happens? Where are the rules to convert a human to a vampire?
You mostly gain extra dots to "catch up" to a newly-rolled vampire character's Attributes, Abilities, and Disciplines, but without the full flexibility of the process of creating a new character.
I'm not clear on how supernatural kinfolk themselves necessarily are, save for potentially passing on lycanthropy to their offspring. The question itself distinguishes between them and ordinary humans, implying that they aren't standard-kit mortal humans. Typically in oWoD supernatural qualities don't mix very neatly, so if your setting and game treats kinfolk themselves as ordinary humans then they should respond to the Embrace in that same, ordinary human mode. This obviously excludes kinfolk that are wolves, as animals cannot be Embraced.
The degree of "supernatural-ness" may vary by individual. WtA is not my specialty, but as I understand it kinfolk do not have the spiritual component to truly be werewolves themselves, but may have some limited access to Gnosis or Gifts. Such access may or may not indicate someone who is sufficiently "werewolf-like" to suffer complications from the Embrace.
So, for kinfolk, the Embrace may or may not be fatal. Well, the Embrace is always fatal, but Garou almost never rise again as vampires (the Curse of Caine doesn't mix well with other supernatural natures, be it werewolf, mage, changeling, mummy, promethean, demon, or anything else). I'm not aware of any rules which define this enough to draw any brightlines, so it's up to the Storyteller if they can experience a human-type Embrace or a Garou-type Embrace.
There are very rare cases in which the Embrace is successful with a Garou, and the resulting werewolf-vampire creature is referred to as an Abomination. Few of these exist in the game's lore, but those that do are extremely powerful and dangerous. They are also usually consumed with a death wish due to their self-loathing, but that's heavily story-dependent. The best reference I found for this is from Under a Blood Red Moon, Appendix Three: The Abominations.
A Garou who undergoes the Embrace of a vampire will most likely die. [...]
When a vampire Embraces a Garou, the Garou must make a Gnosis roll (difficulty 9). If it succeeds, it dies a quick and painless death. If it fails, it suffers a slow and painful death. [...]
Only Garou who botch their Gnosis rolls become Abominations. (Under a Blood Red Moon, page 94)
There are mechanics in that same book describing what happens mechanically, should a Garou "survive" the Embrace, but reproducing those rules here goes well beyond the normal excerpt practice for this stack.
This depends a bit on how the Embrace fits into your game. From what's written in the question, it seems as though you are specifically not creating a vampire character at the outset (and so the "normal" character creation process for VtM doesn't apply).
The case covered in the V20 Core Rulebook (page 500) is for ghouls, rather than ordinary mortals, but the process should be essentially the same:
The character gets additional dots to put into Attributes and Abilities sufficient to make them equivalent to characters who start as vampires (see V20 Core Rulebook, page 80 for a summary).
Presumably these should track with the category priorities for Attributes and Abilities (7/5/3 for Attributes, and 13/9/5 for Abilities), and should also observe the restriction on Abilities that none be raised above 3 in this process. This is not clearly expressed in the rules that I can find, but the "raise them to the starting values for vampires" suggests that your Embrace shouldn't give you special advantages in this particular aspect.
Your Storyteller may impose restrictions on where you can put those dots (being Embraced wouldn't suddenly give you a college education you didn't have before, so they might restrict you from putting your dots in Academics, for example). This is an Embrace, not character creation.
You get dots to put into Disciplines, just like a character starting as a vampire would get (see V20 Core Rulebook, page 80 for a summary).
You get three dots to invest into Disciplines. These Disciplines must be in-clan-- this is a direct product of your character's Embrace, not a freebie point free-for-all. If your character was a ghoul that has learned other Disciplines, you get to keep those in addition to your three new dots.
You gain access to a few elements on a vampire's character sheet that may not have been on your mortal character sheet.
If your character wasn't a ghoul, they'll get new access to a Blood Pool. Starting Blood Pool is determined by a single d10 roll, though that is easily modified by specific, in-game circumstances.
If your Storyteller uses the Bearing mechanic, you'll fill in the Bearing section underneath your Humanity/Path rating.
Certain Merits and Flaws may change, depending on specific circumstances.
Some Merits and Flaws don't make sense on a vampire, or at least become inert. Similarly, your Storyteller may assign new Merits or Flaws based around your Embrace. Examples include New Kid, Infamous Sire, or Prestigious Sire which might now apply to you. This is 100% up to your Storyteller-- you don't get to choose them, and you don't get any new freebie points with which to buy them.
You gain the ability to soak lethal damage in addition to bashing damage.
This doesn't show up on the character sheet directly, but will change how you mark off damage.
Nothing else changes, at least not as a mechanical result of being Embraced.
Your Virtues and Backgrounds don't change, nor your ratings in them, nor your Willpower pools (temporary and permanent). You are the person you were before, you just now have some additional features.