Uniformly charged solid sphere (total charge Q, radius R): Outside (r >= R): E = $\frac{kQ}{r}$^2 (same as point charge at center). Inside (r < R): E = $\frac{kQr}{R}$^3 = rho*$\frac{r}{3*epsilon_0}$. Field increases linearly from center to surface, then falls as 1/$r^2$.

Conducting sphere (charge Q on surface): Outside (r >= R): E = $\frac{kQ}{r}$^2. Inside (r < R): E = 0 (charge resides only on surface). Surface: E = $\frac{sigma}{epsilon_0}$ just outside.

Concentric shells: Apply Gauss's law region by region. Enclosed charge changes at each shell boundary. In the conducting material of each shell, E = 0, which determines induced surface charges.