Once in a graphical environment, you can toggle between it and a
console. Let's say you want to use tty2 (tty1 being busy):
Press Ctrl+Alt+F2, then login.
Press Ctrl+Alt+F7 to go back to the graphical environment.

To know how to use Orca, including its specific key bindings, type:
man orca
In short, once in a graphical environment, in desktop mode:
Insert+Space: launch the orca Configuration dialog.
Insert+S: toggle speech on and off.

The same general key bindings are used in all graphical environments,
with a few exceptions, Mod1 being generally the left Alt key:
Mod1+F1: panel's application menu.
Mod1+F2: pop up a 'run..." dialog, but in Fluxbox (starts lxterminal).
Also in Fluxbox, Mod1+F3 restarts Fluxbox.
Mod1+F4: closes the raised window.

The panel's application menu has the same layout in all accessible
graphical environments shipped but MATE. From top to bottom:
Terminal emulator: mate-terminal in MATE elsewhere lxterminal by default
File manager: Caja in MATE elsewhere PCManfm by default
Web browser: Firefox by default
Mail client: Thunderbird by default
Preferences
Slint Dashboard (non accessible yet as it's a Qt4 app)
Applications sorted by category
Run dialog
Logout dialog (also allows shut down and reboot)

You can use arrow keys to navigate in the menu.

In MATE, the top panel includes on its left from left to right the menus
(Applications, then Places, then System) then launchers for
mate-terminal, caja (file manager), Firefox, Thunderbird and the geany
text editor.On its right still from left to right a notification area,
a screen locker, a logout and a halt or reboot buttons.
The bottom panel has from left to right a windows list, a "show destktop"
plugin, then a workspace switcher.

Still in Mate, partially sighted users can use the compiz window instead
or marco which is the default.

As a regular user, type:
gsettings set org.mate.session.required-components windowmanager compiz
To go back to marco:
gsettings set org.mate.session.required-components windowmanager marco

This setting will take effect at next start of a Mate session.

Or to make the change just for the current session type:
compiz --replace &
and to go back to marco:
marco --replace &

The replacement will be effective immediately

This setting is also available graphically from mate-tweak, in the
Windows category.

You can access specific Compiz settings just typing:
ccsm &

Documentation, including  about accessibility features, can be displayed
from Slint just typing 'slint-doc'

You can configure speech-dispatcher typing as regular user:
spd-conf
Important: when following line will be displayed:
Default audio output method [pulse] :
after : type alsa then press Enter, else you will lose speech!
This is because speech-dispatcher in Slint includes only an alsa plugin,
not a pulseaudio one.

You can configure brltty editing as root this file: /etc/brltty.conf