The answer really depends on what you are hoping to get from the oats.

You may notice your malt extract say something like "non-diastatic, unhopped, pure malt extract", or something similar. Diastatic power is the ability of a malt to convert starch to sugar. In an extract, you don't need it because it's already been converted for you. However, to get starch to turn into fermentable sugar, a diastatic malt is required. The typical malt with the high diastatic power is 2-row.

Adjuncts (such as oat), on the other hand, do not have this power on their own. That said, they can piggy-back off of the enzymes in a diastatic malt such as two-row to perform the conversion and get fermentables. This is why you may have heard that you need to use 2-row along with the oats. A 1:1 ratio should suffice.

That said, the use of oats in an oatmeal stout is not primarily as an adjunct grain for added fermentables, but rather to be used as a steeping grain for mouthfeel. If this is what you're going for, you really can just steep the oats as you would any other steeping grain like, say, a crystal malt.

On another note, oats will turn into a gummy mess, so if you don't need the added fermentables, I would suggest steeping with a grain bag for easy cleanup.

You may notice your malt extract say something like "non-diastatic, unhopped, pure malt extract", or something similar. Diastatic power is the ability of a malt to convert starch to sugar. In an extract, you don't need it because it's already been converted for you. However, to get starch to turn into fermentable sugar, a diastatic malt is required. The typical malt with the high diastatic power is 2-row.

Adjuncts (such as oat), on the other hand, do not have this power on their own. That said, they can piggy-back off of the enzymes in a diastatic malt such as two-row to perform the conversion and get fermentables. This is why you may have heard that you need to use 2-row along with the oats. A 1:1 ratio should suffice.