Brick Blocks are starting blocks in Super Mario Maker. Power-ups, enemies, Coins or Vines can be put in them, much like Question Blocks . They break after being hit by big Mario, or any power-up that makes Mario bigger, unless they have something in them, in which case they become Empty Blocks. The Brick Block is replaced by the Rotating Block in the SMW skin, acting much differently than the regular Brick Block.
The Brick Block can be broken by the Thwomp or a thrown Shell, and turns into a Coin (if empty) under the effect of a P-Switch. It can also be broken by a Bob-omb and more. But if you are small Mario with a helmet, You can break Brick Blocks but most blocks with a spike helmet.