In the first signature, you've just entered the inner fold on the last station of that signature. From here your going to drop down and exit the fold by enter the next station DOWN.
Pull the needle and thread through the signature but NOT through the spine.
After you pull the needle and thread through completely, you'll bring the 2nd signature over,line up the stations with the already attached signature and then enter the 2nd station down from the top. After you enter the 2nd station on the 2nd signature you'll pull the needle and thread the whole way into the fold of signature number 2.
You'll then exit the top station in the signature, and go through the signature and the cover!
Pull the thread tight and work down the spine in the opposite direction you originally were sewing the first signature. If you line up the thread and hold it against the spine with your thumb it's much easier to line the threads against the spine, making them even and equally tense.
After this repeat the process of sewing up and down the spine and climbing as you just did, for the number of signatures you had.
I'll load up a page of helpful hints next!