Underdog is a fantasy platform, not an online sportsbook. You cannot find wagers like moneylines, point spreads, futures, or props. The only Underdog format that resembles traditional sports betting is the Pick'em format, which allows you to build parlay-style contest entries using player totals or player head-to-heads.
Apart from the Pick'em game mode, Underdog allows you to join fantasy leagues, which are divided into two types: Best Ball (season-long leagues) or Battle Royale (short-term daily/weekly tournaments). In these contests, you pay an entry fee, draft a team, and earn a payout if your team performs best.