Particles themselves are just models of localized field quantizations. It's a bit analogous to how a person is just a quantification of the molecules they compr

Particles themselves are just models of localized field quantizations. It's a bit analogous to how a person is just a quantification of the molecules they comprise. You can gain and lose new molecules by the millions, but you're still the same person -- like the crest of a wave. Anyway, particles repel because that is the nature of the fields they exist in. Electrons don't have to do anything 'to' each other to repel, they just have to interact with the electromagnetic field. The string model simply employs the word 'string' to describe some components of the field.