- Will the lens hood increase the photo quality?
In general yes, but not always!
If the sun is in your field of view, then unfortunately, the lens hood cannot block that. Also, at times, if you happen to have a UV filter on and then a hood on top, this can at times create vignetting. It doesn't happen with all hoods, but can do so with some after market models.
Also, with some zoom lenses, you may find that you still get flares and unwanted reflections if you are using a petal hood and have the camera in a vertical orientation. I quite often find myself turning the hood or using a newspaper to create a shade.
- What are the types of lens hood?
Most common are, Petal; used for wider angle primes and zooms, and complete circular with felt interiors, used for larger primes and Zoom lenses.
Wider angle lenses need the extra cutout on each side to allow for the maximum width of the lens.
- Should I be looking at a "petal" lens hood or a circular one?
For the 18-55mm, you need to be looking at a petal hood in order to ensure that no light is blocked from either side and therefore you are capturing the complete image.