(A) ADVANCED: This section is aimed at advanced users.
The BaseCollisions component controls the basic interactions between a character and the level geometry. It stops the character falling through floors, running through walls and jumping through platforms. It uses the RaycastColliders and layer settings to calculate this behaviour.
Some movements do not apply base collisions instead applying their own rules. See Writing Custom Movements.
The BaseCollisions component has no settings and for most users will never need to be considered. However you can override the BaseCollisions class and provide your own behaviour if you have very unique requirements.
Warning: Customising the BaseCollisions can have wide reaching and hard to determine ramifications on the system. Handle with care!