Unlike many other games, these expansion cards don't really add any new major gameplay rules, more so just new abilities and effects. You simply mix and match the new non-essential cards with old non-essential cards during deck construction. So, the basic game rules already include any new elements introduced in the expansions like the Start of Game trigger event and the Forked Path attribute on the Galdor/Feragot card.
Viewing post in Bundle Did not include rules for 3 expansions
Ah yes, correct. The first 18 are the core set, next 6 are E1, next 6 are E2, last 6 are E3. It may be tough to see but the text on the bottom left lists the set a card belongs to. The inverted text over the black background bubble says "Core Set". The following sets say the expansion name and have "(E1)", "(E2)", or "(E3)" next to them.