Parts are an important aspect of a vehicles in Grand Prix Story. When attached, they raise certain stats/provide specific bonuses, that the vehicle would otherwise not have.
Once gaining access by Y1, M6, you can then begin researching and upgrading new parts & vehicles using Research Points. Once researched, parts can be attached to any assembled vehicle in your garage. Upgrades and level ups increase the effects of parts, which have a variety of different benefits for each type.
When installing a part, it is also important having a good team install it. Higher ranked parts can be difficult to put on quickly and correctly for a team with low combined tech. A very high tech can make quick work and even make parts perform better than normal. Auras can also give a temporary boost to the effectiveness of the team when attaching parts.
Upgrading is important in making sure your part is in prime condition. When you upgrade a part, you increase most, if not all of it's given stats. Each part can be upgraded 5 times, with each upgrade costing more Research Points each time. Using auras, especially gold, is an important part, as it increases the amount the upgrade enhances. A team's tech only effects the time it takes to apply the upgrade, not the amount upgraded.
For unlock conditions, when sponsors are listed that means that to obtain the part you must have maxed-out that sponsorship, when a part followed by a percent is shown, it means the part is unlocked when the listed part is upgraded to the listed percent, and when races are listed, you must finish them in first place.