I brew AG but have done some partial or mini mash recipes.
Steeping the specialty grains essentially replaces the bashing step used in AG. You're extracting the sugars in your grains then rinsing the steeped grains (sparging) to rinse out any residual sugars & stop any enzymatic activity. It's a fancy tea for all intents & purposes.
The specialty grains, depending on how much they've been killed/roasted add color, flavor, body, & can aid in head retention.
You replace the balance of the sugars you would have gotten from mashing by adding either DME or LME, sometimes both, depending on your recipe.
Next you boil & add hops per the recipe, chill, transfer to your fermenter & pitch your yeast.
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