The rapport describes what kind of relationship you have with a companion. Every companion has personal preferences which will affect how they feel about the player over time, based on their actions. Acting against a companion’s ideals will cause their rapport with the companion to decrease. Taking actions they favor will drive the player’s rapport with that companion up.
While this has no effect on their skills or their abilities, it will have an effect on their gameplay. At least when it comes to extremely disliking the player. If a companion hates the player, they might not be able to stand them much longer and will unsummon themselves for a while.
In order to build rapport with a companion, performing average actions is a must — either by questing, leveling or other in-game actions like stealing. This can go both ways, so the player should be aware of what they like and what they dislike.
The more a companion likes the player, the more personal quests become available to the player after having completed the initial quest.
