How to manually focus properly with Nikon D3300 and 70-300mm lens?

How to manually focus properly with Nikon D3300 and 70-300mm lens? - 1

Simply put, you rotate the focus ring until the part of the image you want in focus looks sharpest.

You can also use the Focus confirmation dot at the lower left corner of your viewfinder.

D3300 doesn't have a focus motor, so you must focus manually or get a higher end camera like the D7000/D7100/D600/D750/D810 etc, OR a lens with a built in AF motor like the 70-300 AF-S G VR. I suggest the 55-200, as it is very cheap and has VR, ED and SWM.

Set focus switch to MF or M then turn focus ring.

It will be more difficult and often less accurate than autofocus. Also the cheapo 70-300mm that you got
http://slrgear.com/...122/cat/13
will never have the sharpness at the long end of the lens that you should have saved your money towards.
http://slrgear.com/...992/cat/13

Page 83 of your manual tells you how to put the lens in Manual focus mode.

Page 248 of your manual explains how to use the Rangefinder in your camera.