Complex sentence: Colonel Brewster is mortally wounded by the T-X, as she arrive in time before John, Kate and the Terminator arrive, before dying he gives Kate and John a code book and the location of what John believes is Skynet's system core.
Split into simpler sentences: Colonel Brewster is mortally wounded by the T-X, as it arrived before John, Kate and the Terminator. Before dying he gives Kate and John a code book and the location of what John believes is Skynet's system core.