I'm no expert Kunohara, I can only tell you what worked for me.
To start with I spent way too much time reading the manual and fiddling with settings and taking the odd picture before I realised the photography is essentially an
experimental art. You learn it by doing it. I learned that the hard (but fun) way by spending three hours wandering around taking photos in heavy mist where none of the auto settings worked at all well.
For online resources I'd suggest the following:
Dan Heller: A lot to go through, but worth taking your time with
Photozone.de: very thorough, very detailed, very useful (but maybe after you've got the hang of the basics)
Ken Rockwell:Interesting, provocative and sometimes annoying, but he does seem to know his stuff and usually fun to read
But the main things are to:
(a) keep off the preset stuff on the camera - stick to the 'creative zone' of Av Tv and Manual
(b) Get the hang of paying attention to the numbers in the bottom bit of the viewfinder so you know what you are shooting at
(c) Try some difficult things. Mist, nighttime, indoor still life. And see what works.
Also, you might consider (and what worked for me) turning
off Auto-ISO. Stick with ISO 100 for daytime and ISO 400-800 at night. It's one less variable to work with and helps you work out what to do with aperture and shutter speed. If you have auto-ISO on the camera always tries to compensate and you can't necessarily see the difference that you have made, until you get more in the habit of looking at photos and seeing what is in them.
EDIT: The other thing worth considering is photography magazines. There's a lot of them, but the DSLR Bootcamp in
Practical Photography (which ran over about six months last year and I think is an annual thing) is quite a good gentle introduction to the basics.