First, welcome to the best LCG!

To get started quickly, if you have a single core set, it is assumed that you use the quick 'deck-building' rules described in the core set. I.e. you combine the cards from two factions ( 20 cards each*) with seven of the neutral cards (the neutral conspiracy is not used).

While these 'starter decks' are not tournament legal, they are sufficient to learn the rules and get to know the factions' capabilities.

Once you have more cards, you can mix any number of factions in a single deck and should stick with a minimum of 50 cards.

*: Note, that due to a misprint, the Miskatonic faction is one card short: Steve Clarney has been accidentally assigned to the Agency faction. But as long as you are still playing casually, you could treat him as a Miskatonic character, if you prefer.

Many thanks. That clears that up. For now I will probably just be playing against my wife or daughter at home, and roping some friends into playing with my cards. I will be re-watching those great videos as well that FFG have put out.