Understanding Aperture & ND Filters

abtiwari

Hi,

I use a Canon 60D for my hobby photography and I use two lenses.

1. Default Canon 18-55mm IS kit lens
2. Tamron 16-300mm PZD Macro Zoom Lens

I can still not understand the best aperture settings for various shots.
I cannot maintain an eye-level from a distance with the camera being handheld, to take portraits.
I want to know the right ND Filter for taking 'silky' shots of a waterfall in bright sunlight.

Please guide, thanks in advance.