This is a bit simpler to explain than what we'll get into next, but is also considerably more expensive to do more than every now and then. Still, you may not always be able to get the yeast out of your yeast bank (or that of someone you know, a club yeast bank, etc.), and may have to order it.
Follow the yeast lab's instructions to start up the pack/vial that they send you. Whether you use prepared sterile wort for starters, or do it the hard way and make starter wort every time, you want about 300—400mL of wort here per 6 gallon batch size.
Using your O2 bottle and (cleaned/sanitized) oxygenating stone, oxygenate the starter wort, swirling it around to help it absorb the oxygen rather than foaming up too quickly, to a point where no matter what you do, it's foaming up, and you're running out of space to pour in the yeast. At that point, quickly remove the oxygenating stone and turn off the O2. Pitch your yeast from the yeast lab into the wort. Do NOT add O2 after pitching the yeast! Cap the Erlenmeyer flask off with a stopper and an air-lock. Use some type of sanitizer in the air lock. Some will call this excessive, but I prefer to use cheap vodka in the air-lock, just as I use Everclear (or the generic equivalent) as a food-grade alcohol sanitizer (which just happens to be at the max-kill level for alcohol, too---anything above or below roughly 73% alcohol has a reduced percent-kill relative to approximately 73%).
Following the same basic procedure as above, transfer the roughly 220mL starter that you made from the 10mL starter you made from a slant into an Erlenmeyer flask and, using starter wort as above, bring the level in the new flask up to a level which, when added to your starter, will bring the total up to your final pitching quantity. Using pure O2 as above, oxygenate your new starter wort, add your starter to it, and cap with an air-lock as above.