Your team has 7 infrastructure departments, each with 10 levels. Level 1 is “rookie team out of a garage”; level 10 is “championship-grade operation”. Upgrading costs money up-front and unlocks ongoing perks (more WU, better fiability, sponsor scouting, etc.).
This page will list every department, what level 1 → 10 actually unlocks, and the recommended upgrade order for Small / Medium / Large budget tiers.
In the meantime, Sponsors explains how Marketing levels affect sponsor scouting; Parts, Damage & Wear explains how Engineering affects repair efficiency.