Pharmaceutical grade dry agar for making plates and slants. 2 oz will make up approximately 4000 ml of liquid agar. BK580, First Steps In Yeast Culturing, is a great reference if you do not have prior experience working with agar.

For lab use, use 12 grams to make 1 liter of solid agar, which is way more than even a big laboratory uses. You need a very accurate scale to measure that out. You want to dissolve the agar slowly in the water or wort for a few minutes. Then heat gently till you get to a boil. Be very careful of not boiling over, if you do it's best to throw that boil out as your water to agar ratio is off and you will not get a good medium. Boil for a few minutes and then divide out to sterilize.