Simple binds (move, fire, jump..) can be done within Unreal Tournament's interface using the menu Options / Preferences / Controls (pic.1)
You can also use the Advanced Options (Options / Advanced Options / Advanced / Raw Key Bindings as shown in pic.2).

Complex binds (several commands assigned to just one keystroke, or "alias") can also be created inside the Game, using Options / Advanced Options / Advanced / Key Aliases (pic. 3)

Important point #1 :
Every modification you make will be written in the file User.ini in the System directory (e.g. C:/UTdemo/System). My advice is that you create a backup of this file, since there is no "Undo modifications" feature provided. Don't overwrite a complex alias if you have no backup copy.

Important point #2 :
The "Reset to Defaults" button you may see in the interface simply overwrites the content of User.ini with DefUSer.ini.
When your personal config user.ini is more or less something you are used to, my second piece of advice is that you delete DefUser.ini, copy User.ini and rename it to DefUser.ini. By doing so, you will be able to reset your config to *your* default.

(pic. 1)

(pic. 2)

(pic. 3)

I find it easier to edit User.ini than to use the graphic interface.

If you still want to use the graphic interface, here is how it works :
- bind a key to the alias NameOfYourAlias using the menu Options / Preferences / Controls (pic 1) or the Advanced Options (pic 2)
- then define your alias, i.e. define its name (Alias) and what it does (Command) (pic 4)

If you feel more like editing your User.ini, most of what you'll modify belongs to the [Engine.Input] section, that contains the alias definitions, then key binds.

Aliases[number]=(Command=" <what it does> ",Alias= <NameOfYourAlias> )
<Key>=NameOfYourAlias

For example :
Aliases[22]=(Command="Say I am the best ! | Taunt Victory1",Alias=SoGood)
Space=SoGood

When Space is hit, your player says "I am the best" and shows he means it :-)

NB : you can only create aliases numbered from 0 to 39, no more.

NB : read the file User.ini, as all keys available for bindings are mentioned. However, UT doesn't seem to recognize Right Control and Left Control, although these are mentioned in the file (as RCtrl and LCtrl). Same problem with LShift and RShift.

(pic.4)