Unmodified, the oxygen of alcohols and ethers is a miserable leaving group - but reaction in strong acid protonates the oxygen atom and makes it a good leaving group. Otherwise, the chemical reactions are very similar to those in chapter 7. One electron goes to each side. The periods represent one electron from the R-Br bond. Since ions are not formed, and the radical species are electrically neutral, electrostatic forces play a much smaller role in radical chemistry.
Radicals form resonance structures in the same way that ions do.
You get a new radical species and the chain is propagated. There are usually a lot of possible propagation steps. Propagation steps depend on there being a supply of radicals already present. Radicals can react with alkenes and alkynes in much the same way that electrophiles do, like hydrogen ion. Section 4.8 give an example of how this can lead to very long molecules - polymers.