An ideal solenoid (infinite length, tightly wound): inside $B = \mu_0 nI$ (uniform, independent of position), where $n = N/L$ is turns per unit length. Outside: $B = 0$. At the end of a finite solenoid: $B = \mu_0 nI/2$ (half the interior value). The field inside is parallel to the axis. The solenoid behaves like a bar magnet externally. A solenoid with $n$ turns/m and current $I$ produces the same field as a bar magnet with surface current density $nI$.