Redstone Torches vs Blocks
These examples use redstone lamps to show the difference between redstone torches.
A redstone block is powered, and switches on the blocks that are directly next to it.
A redstone torch powers the block that contains it, and also powers the block above it (labeled 'A'). This means that blocks next to the torch are switched on, and also the blocks next to the one above.
Most redstone power sources power two blocks; usually the block they are in plus the block they are attached to, but blocks of redstone (along with daylight sensors) are an exception.