Dawkins´s Definitions

Survival machines: "The ones [Replicators] that survived were the ones that built survival machines for them to live in." (pg. 19)

"They have come a long way, those replicators. Now they go by the name of genes, and we are ttheir survival machines." (pg. 20)

"We are survival machines, but "we" does not mean just people. It embraces all animals, plants, bacteria, and viruses." (pg. 21)

"Now, natural selection favours replicators that are good at building survival machines, genes that are skilled in the art of controlling embryonic development." (pg 24)

Basically, survival machines (humans, animals, viruses, and bacteria) were built by genes so they could live in. The genes which are most succesful controlling embryonic development have survival machines which will live more in terms of natural selection.

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Replicators: "At some point a particularly remarkable molecule was formed by accident. We will call it the Replicator. It may not necessarily have been the biggest, or the most complex molecule around, but it had the extraordinary propety of being able to create copies of itself. (pg. 15)

"Actually a molecule that makes copies of itself is not as difficult to imagine as it seems at first, and it only has to arise once." (pg. 15)

"For simplicity I have given the impression that modern genes, made of DNA, are much the same as the first replicators in the primeval soup."(pg 21)

Well, these excerpts explain what a replicator is, no need of repeating what is already known.

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Evolution: “Evolution is something that happens, willy-nilly, in spite of all the efforts of the replicators (and nowadays of the genes) to prevent it happening.” 

"Anyway, as we shall see, erratic copying in biological replicators can in a real sense give rise to improvement, and it was essential for the progressive evolution of lif ethat some errors were made." (pg. 16)

"Their [Replicator] modern descendants, the DNA molecules, are astonishingly faithful compared with the most high-fidelity human copying process, but they ocassionally make mistakes, and it is ultimately these mistakes that make evolution possible." (pg. 17)

Evolution happens when DNA copiers make a mistake and these mutations have positive effects on the gene, making natural selection benefit it´s survival. The more mutations in a gene pool, the higher variety in evolution and different types of replicators in it.