You have 2 options
1) Make a table, but do not choose any cards to go into. Wait for an opponent to join (or have a friend join you with whom you have arranged this previously). Then start a game, the server will fill in the cards randomly from all player's subscriptions. So you can use the cards you are subscribed to.
2) Got to the automatch screen (the one you land on after you login) and search for a game against a random opponent. Here you can see settings that may allow you find an opponent quickly:
Make sure your Level in the "Card Pool Level" pane is at 5 (for a Core subscription) or 10 (for a Complete subscription).
Make sure that the buttons in the "Rated games" row look exactly like shown. You can, if you want, also also allow extra 2nd Edition games and/or join a 3 player game.
Using +10 and -10 for (relative) rating allows you to draw from a large pool of players, but you may get players that are much stronger or much weaker than you. Reduce this to maybe -5/+5 or even less if you want to avoid that (with the risk that a smaller number or no players are available.
Then press on "Start Search" and the server will try to match you with a random opponent who also looked for a game this way. Like in option 1, it will select the cards from what any of the participating players have subscribed to.