Sorry if my hyperbole was confusing. I'll write you a prescription.
Study a small portion of your T6i manual every day until you have
gone through all relevant parts of it and then start again and repeat
as needed. The basic principles of photography, regardless of which
subject matter excites you, is a COMPLETE understanding of the relation-
ship between film sensitivity to light (now sensor-sensitivity) and the
quality of the image. Increasing sensitivity (speed) decreases image quality
through several related trade-offs. That's how you decide what sensor speed
is worth using in any particular situation. Flexible shoes are more comfortable
that stiff shoes but they also wear out faster. It's a trade-off.
The second basic principle is the relationship between lens focal length
(power) and lens diameter (light gathering ability). That relationship
is called the speed of the lens (f-stop). The faster the lens the more light it
collects and the faster your shutter speed, or the more you can reduce
your sensor sensitivity (ISO) to get a better quality product. Some lenses
boast a lot of power but they are fairly slow and don't let in much light.
The lenses that have both power and speed are the Jimmy Choo's of the gear world.
Some shoes look really cool but they are all synthetic, make your feet sweat
and promote fungus. All-leather upper and lowers may not deliver the same
wow factor but they will last a long time and your feet will love you for it.
The back button focus on your camera can be set through the menu so that
you focus not by lightly pressing the shutter button but be pressing one of
the tiny buttons on the upper right back of your camera using your thumb.
That way you can set the focus and when you touch the shutter button to
set the light (aperture - f stop) the focus doesn't re-set itself every time.
Although it is work, you should practice exposure compensation to the right
and left of center. Hold down a small back button and turn the wheel either
right or left. Turn left to darken the subject and manage highlight over-exposure (if there
are a lot of highlights in the subject), and turn right to open the lens to make
your Kingbirds better exposed. Your camera light meter sees the bright sky and
chooses to close your lens iris to deal with the brightness. By over-riding that
with a right side compensation (deliberately re-opening the iris) you are saying
to the camera, hey, wait a minute, I don't want you to short-change by birds,
so back off and let the light shine in! Just don't forget to re-set afterwards or
your next non-sky oriented shot will be over-exposed and your camera will retaliate
by ruining your subsequent efforts. Back-talk to a camera is a risky endeavour.
The third basic principle is the relationship between f-stop and depth-of-field.
The more you close the lens iris the more the field of stuff in relative focus becomes.
If your bird is really close you would want to shoot at f8 so that most of the bird is in
focus. If it is far away then you can open the lens more, even wide open and the whole
bird might still be in focus. When wide open the depth-of-field is shallow. There is
really only one plane of sharp focus, but the depth-of-field represents the stuff behind
and in front of that plane of focus that still looks in acceptable focus. If your bird is
close and you shoot at f7.1, or f8 then your shutter speed might be too slow so your
crank up your sensor sensitivity (ISO) to compensate. Poorer image quality but the subject
is so close that you don't need to crop much and the drop in quality might therefore not
become as apparent. I always have to crop because of my measly 200mm power limit
so a high ISO setting really shows image noise and grainy artifacts just like the olden
days with FAST film emulsion. You get the shot but the picture is grainy, and has a narrow
exposure latitude (meaning its contrasty ... no shadow detail and no highlight detail).
High ISO does the same thing and it shows up when you crop in heavily. This may be a
moot point with a 600mm behemoth. A year from now I'd hate to arm wrestle you.