Hope this is not a silly question
 

Not a gear head but have been reading about something called
direct fuel injection. i understand what fuel injection is. so what is the difference. and does it increase horsepower............

DI involves injecting fuel directly into the cylinder rather than into the intake tract

What he said... gives a more precise mixture of fuel/air.

It gives a cleaner burn and has been shown to increase HP on some vehicles like the CTS as well as being able to burn a lower octane with no decrease of HP or risk of knock.

It gives you better fuel atomization as the fuel is able to be sprayed in a more precise pattern directly into the cylinder which allows for a more complete burn, hence why it yields fewer emissions and more power since more fuel is being burnt for the same amount injected.

There are negatives (I know it is true for the Audis, but not sure about brands)......
The lack of fuel flowing over the intake valves can lead to dirt build up on the valves. Mosr fuels have cleaning additives that clean the intake valves.