The redstone block is a block made from 9 redstone dust and is an infinite power source that cant be deactivated unless not touching any other redstone components.
Pistons are a component used to push other blocks around with a sticky varient to puck and pull other blocks when powered.
Observers output a signal whenever they detect a block update or movement making it very useful for crops as it will detect when they have grown.
Comparators are used to measure the amount of items inside a container by putting out a redstone signal based on the how full the container is.
Repeaters are used to control the speed of a redstone current or continue the power of the redstone for a further distance.
Hoppers are used for the transfer of items between containers and can be used to collect dropped items if they fell on a hopper.