How do I know where my XOR gates go? What does the F2 stand for here? Also the next task is to generate the sequence (with initialisation vector $s_0 = 1, s_1 = s_2 = s_3 = 0$) until it becomes periodic which I'm fairly certain I can do however even a few rows would be helpful as I won't have any other answers to these (not official homework assignment).
edit: my guess is now the xor port goes on top $s_3$, because of unknown reason. How will this affect the sequence? When generating it I shift and do I xor the last $s_3$ and first $s_1$ in order to receive the new bit?