All interactions between standard model particles are essentially the same in string theory. It's just that you can say more in string theory about what the particles and fields are.
For example, electrostatic repulsion will have a description in QED, in terms of quantum fields and virtual particles. The explanation in string theory should be identical up to a certain point, but the "virtual photons", etc, would actually be particular string states.
For reference I mention "QED and string theory", which aims to realize just QED, via open strings stretched between space-filling D9-branes and a four-dimensional "probe" D3-brane. The real world contains many other forces and particles, and so the string models are accordingly more intricate.
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