Right, so I have gathered that once you pick a talent this determines what talents you can pick next; the ones connected via the lines.
Does this mean that if I go for the smuggler scoundrel tree and pick black market contacts, I have to go for convincing demeanor (at 10xp) as my next talent from that tree? What if I start out by picking quick draw. It has no lines connected to it… should I then just pick another 5 point talent and go on from there?
I find these trees to be slightly confusing.
They are a bit daunting at first, I'll grant you, but not horribly so.
The main question in determining if you a talent qualifies as a prerequisite is "does the talent I want have a grey line connecting it to a talent I already have?" The only exception are the first tier / 5 XP talents, as those can be taken at any time.
So for your example, if you take Quick Draw, then you can't take any of the 10 XP talents because Quick Draw doesn't have a line connecting it to to any other talents. But if you take Black Market Contacts, you can buy Convincing Demeanor because they are connected by a grey line. But you couldn't by Black Market Contacts for 10 XP because there's no connecting line between the Convincing Demeanor talent that's one the 2nd row of the leftmost column and the Black Market Contacts that's to it's immediate right.
Let's try another example, the Thief talent tree on the adjacent page. Let's say that your character has already purchased the Bypass Security, Indistinguishable, and Street Smarts talents from the first row.
You'd be eligible to then purchase the following 2nd row talents: Black Market Contacts (connect to 1st row Street Smarts), Grit (connected to 1st row Indistinguishable), and Hidden Storage (connected to 1st row Bypass Security), but not Street Smarts because you don't have Black Market Contacts on the 1st row. But, if you purchase either Grit or the 2nd row entry for Black Market Contacts, now you can purchase the 2nd row entry for Street Smarts because BMC and Gri are connected to it horizontally.
Also, the lines are not one-way arrows. So for trees like Scoundrel and Force Exile, which require you to to buy up to some rather high-level talents before you can access the middle cluster of talents, once you get those high XP talents from the bottom rows, you can follow the grey lines back up. For example, your Scoundrel manages to have purchased Dedication and then Natural Charmer. He can then travel back up, buying Rapid Reaction, which then connects him to Toughened and Hidden Storage, and so on.
I hope this helps, and apologize if I've only managed to confuse you any further.