in options select controls then advance then allow console prees ` (topp left button below escape) and type
sv_cheats 1
to allow cheats then
impulse 101 to give all wepons

Open the developers console by pressing the ` button, and type in "upgrade_portalgun".

This will give you the portal gun and allow the use of the blue and orange portals.

Enable the console and type sv_cheats 1 to enable cheat use. Below is a list of codes you can put on:

Invincible / God:-
type "god" (without the quotation marks) in the console.

Halflife Guns:-
Type "impulse 101" (without the quotation marks) in the console.

Noclip / No gravity:-
Type "noclip" (without the quotation marks) in the console.

Buddha / 1 Health:-
(stops you from getting below 1 health) type "buddha".

Picker:-
(allows you to see each models boundaries) type "picker".