Competitions on GameDay Squad are free to enter and you can be in up to three standard ones at once, plus specials. Each standard tier has a salary cap and rarity rules, which is how a free Bronze squad avoids meeting someone's million-dollar Legend collection on a leaderboard.
The ladder, roughly
Starter sits at the bottom: Bronze cards only, modest cap, built for new coaches. The tiers above it (through to Champion) raise the cap and open up higher rarities, with Champion expecting Platinum and better. Prize pools rise with the tiers.
Special competitions run alongside: Primetime has no salary cap at all and only covers Thursday and Friday games, the under-22s comp is exactly what it sounds like, and one-off cups appear through the season. Every sport will have slightly different special comps so keep an eye out for guides on the society page.
What we'd actually enter in week one
Starter, obviously, that's where your free squad is competitive from the first bounce. Use your other entries once you understand your card pool, not before. An empty entry slot costs nothing; a half-built squad in a comp you can't win just spreads your attention thin.
Its entirely possible to move up the competitions without spending a cent. As you start to win prizes in the lower comps, they will help push you forward. There are many coaches competing at high levels who have not deposited anything.