Can someone enlighten me on the plot of Half-Life 2/end of Half Life 1?

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Ive been playing HL2 and have been loving it, but i'm assuming that you needed to finish 1 in order to know whats going on in 2, which i never did. cause i'm completely baffled as to whats going on. so could someone tell me the end of HL1? in other words, spoil it for me. and how does it relate to 2? anybody?

 

[TrevJ]

You don't really need to know that much about HL1 to understand HL2. I've played through HL1 several times, and I don't know what the hell is going on in HL2.

During the last few chapters of HL1, you go to Xen, the alien world which acts as a border world for teleportation between Earth and some other world. You whip some ass, and (it is assumed) free the non-hostile inhabitants of Xen, namely the Vortigaunts who are now allied with the resistance in HL2.
At the end of HL1 the G-Man offers you a job, which you can either accept or turn down. HL2 assumes you accepted the job, and at the start of HL2 the G-Man calls you into service again to carry out whatever grand plan he has. Nobody really knows what's going on with the G-Man.
HL2 is set an indeterminate amount of time after the events of HL1, and the Combine have taken over the planet for its resources I assume. The theory is that the Combine were alerted to Earth's presence after you cleaned house in Xen, and came to Earth for revenge and found other benefits.
That's basically all you'd know (and maybe even a bit more) at the start of HL2, and things don't get cleared up much from there.