Very simply - Malted barley contains starch. Yeast cannot eat the starch - it needs to be degraded into shorter chain molecules (sugars).
Some malted barley contains enzymes that will degrade this starch if given the right conditions ( leading to saccharification). Hydration and temperature are the two main conditions that activate these enzymes so soaking in water at the right temperature is enough. This is called mashing. pH is important too but leave that for another day.
These are your base malts like pilsner, pale, munich, maris otter etc.
All malted barley has been wet, and kilned or roasted to various degrees as part of the malting process. Some of it is kilned/roasted to higher degrees than others and is darker in colour. Of these, some have been kilned while still wet which encourages the same kinds of reactions that occur during mashing to happen inside the malt kernel itself.
These are your crystal type malts - crystal, caramel, cara, etc.
Some malts contain no enzymes and need extra enzymes from other grains to convert their sugars. Grains like biscuit generally fall here.
Other malts are kilned or roasted to a high degree. Some level of conversion may occur but generally any enzymes are destroyed quickly by the process and any sugars are burnt off. These are your roasted malts like chocolate or black malt. Roasted barley is unmalted barley that is essentially charred.
If you make beer entirely from grain, you need the bulk of the malt to contain enough enzymes to degrade the starch to sugar for the yeast to eat. When you make an extract brew, the malt extract comes from this process (which is then dehydrated and packaged for you to easily use).
To add flavour and colour to a pale brew (whether made from pale base grain or pale malt extract) you can soak certain malts in water (cold or hot works) which is known as steeping. Very little sugar is extracted in this process (crystal malts will add some), no starch is converted at all. Crystal and roasted malts are known as specialty grains and need only to be steeped. Grains like biscuit are also specialty grains but may need to be mashed with some base grains.
Thus an extract + steeping specialty grains requires no mashing to provide the yeast with the sugar it needs.
You can do a thing called a partial mash in which part of your fermentable sugar comes from mashing base grain and the rest from an addition of sugar (usually malt extract). It's what some people do if they want to get that grain flavour and learn about the processes but have small or limited equipment for mashing.
What grains have you typically been using? The process for the brewer to steep or mash can be identical (soak cracked grain in hot water, boil resulting liquor with hops) but the reactions occurring inside the grain are different.
The reason I say that it will make a difference to recipe is that you might mash 2 kg of pilsner malt but would not steep 2 kg of chocolate malt to make a single batch.
