Flashing LED circuits
It's not a particularly good circuit. The base current to the BC547 needs to be less than actually needed, but not by much, and setting this up is finicky. Too easy for it to simply go into a quiescent state that doesn't oscillate. I guess that's why the pot is added.

A better circuit that's similar but more manageable is:







simulate this circuit &ndash; Schematic created using CircuitLab

No pot required. But you can modify \$R_6\$ to change the timing between pulses. It's also fairly easy to understand. When first powered up, \$C_1\$ has no voltage across it so the emitter of \$Q_1\$ is at ground. The divider pair of \$R_1\$ and \$R_2\$ are sufficient to put \$Q_1\$ active and with its collector pulling towards ground. As it pulls a little, current in \$R_4\$ activates \$Q_2\$, which pulls up on \$R_5\$ adding to the base current in \$Q_1\$ and quite soon pulls \$Q_1\$ fully on and therefore also \$Q_2\$. This leaves the LED ON, of course. Now, as \$Q_1\$ continues to pull collector current, as well as the addition of current through \$R_6\$, this adds to the voltage on \$C_1\$ and the emitter of \$Q_1\$ rises upwards, eventually squeezing \$Q_1\$ off. When that happens, \$R_3\$ helps ensure that \$Q_2\$ is off and suddenly there's no current in \$R_7\$ or the LED and the collector of \$Q_2\$ goes towards ground. This causes \$R_5\$ to pull down still more on the base of \$Q_1\$ ensuring that it is off. Now \$C_1\$ leaks current via \$R_6\$ towards ground through \$R_7\$ and the LED (weak current, too low to see) and \$C_1\$ discharges. As it does, \$Q_1\$'s emitter voltage declines and evenually \$Q_1\$ becomes active again, pulling back up on the collector of \$Q_2\$ and repeating the cycle.