For DNA to have any effect it must first be converted to mRNA prior to being made into a protein. When DNA is made into mRNA, certain changes are made. One of the biggest changes is known as splicing. Consider buying a watch with a metal link strap and finding it is too big. You would have links taken out of the strap and then put the whole strap back together at a shorter length so that it fits. This is sort of what happens to the DNA. When the DNA is made into mRNA certain parts known as introns are removed and the molecule is then put back together to be functional as mRNA. A processed pseudogene is created when this functional mRNA (so no introns) is converted back into DNA, instead of to protein as it should be. This new bit of DNA is then re-inserted to the genome. Due to the lack of introns, this DNA cannot be made into new mRNA, so is no longer functional - a false gene.
As the name implies, this is DNA that is non-functional but not as a result of the process I outlined above. Non-processed pseudogenes are simply genes that were once functional but are no longer expressed. These can also be known as fossilised genes as they were once necessary, but due to lack of use they no longer function, a case of ‘use it or lose it’. An example of this is a gene with the catchy name of OR7D4. This gene (like many non-processed pseudogenes) is part of our sense of smell and in approximately 30% of people it is no longer functional, meaning these individuals are unable to smell a chemical known as androstadienone.
These are genes which have been disabled by some external factor such as a protein which may have mutated and become irreversibly bound to the DNA, impeding its expression.
These are genes which are expressed but have no known function. It is though that these may be early proteins which will evolve over time to have a function in future generations.