I am about to start half-life 2 now that i finished portals up but i was wondering if anyone could give me a quick summary of what i need to know about half-life before entering half-life 2.  thanks in advance. xD

Not much at all.

Gordon started all the events

Gordon is the main character

Headcrabs are from another planet

The G-man is weird/cool and his history is unknown.

You were hired to do what your doing in HL2.

okay, thank you ssj12.

pretty much what ssj12 said nothin more then that

You run around from place to place with people screaming Gordon Freeman, i just saved you 10hours, now you can play ep1

http://en.wikipedia.org/wiki/Half_Life

For any other things that might confuse or interest you.

Oh everyone will apparently know who you are.

beat me to it ^^

What happened in the first game, in a nutshell:

Gordon Freeman is/was a physicist at the Black Mesa complex, a research laboratory for experimental technologies. One day, Mr. Freeman is conducting an experiment. He dons his hazard suit (the thing that basically enables him to survive the forthcoming events) and steps into a chamber to assist with the experiment's progression.

When, suddenly, blammo. These weird little head-crabs start appearing. Some of them try to attack Mr. Freeman; others take over the bodies of scientists and guards, turning them into horrid monsters. Mr. Freeman now finds it's his goal to get out of the place, and in the process he runs into a whole manner of odd creatures, from two-legged squeaking creatures that shoot sonic waves at you to gigantic, tentacled monstrosities that "see" via sound.

Fast forward, and soon this recurring, mysterious character ("The G Man") starts showing up in all sorts of odd places. He's this weird-looking guy in a blue suit carrying a briefcase, and he's always walking away from you on a faraway platform or somesuch.

Later on, you find that the military, for some as-yet-unknown reason, has sent in the troops with orders to kill you. You spend a good part of the game evading them, until they finally back off. In the process, you find that Black Mesa has been experimenting with these "headcrabs" - you even discover a few specimens in what appear to be stasis tanks.

Finally, you encounter a scientist who claims that he knows of a way to stop this madness. He then sends you to Xen, the "border world" (though what it borders other than Earth's dimension remains a mystery...) Freeman fights his way through Xen, culminating in the personal destruction of the super-intelligent and extremely powerful entity controlling the dimension.

At the end, you finally come face to face with the G Man, who informs you that, thanks to your efforts, he has been able to bring Xen under control. He then offers Mr. Freeman a choice: work for him, or die. You can make either choice at the end of the game, but it's assumed that you pick the first, since otherwise there wouldn't be a sequel.

There's likely something that I've missed, but that's all the important stuff.

(Note: The incredible thing is that all of this is told without a single cutscene. There's never a time where you're not at least given freedom of movement.)