Points
A points collection is a cloud of positions, the simplest visual collection, and the thing you scatter, simulate and instance onto.
What a points collection is
A points collection is a collection where every row is a single point in space. Each point carries @P and @id without anything having to create them, and can hold any other column: @Cd for colour, @pscale for size, @orient for a facing direction, a velocity, an age, a custom value.
There are no faces and no connections between points. Join them into faces and you have Geometry (meshes). String them into strokes and you have Curves (lines & paths).
Where points are used
Scatter. The Points node sprinkles points across a surface, inside a shape, or through a volume. One pin takes the region, whether that is geometry, a shape, a distance field, a volume or an image, and picking a preset on it drops the shape node in already wired. Mode says where the points land: Surface spreads them area-weighted over a mesh, Interior fills the inside (a mesh is converted to a distance field for the purpose), Edges walks a shape outline by arc length, Density keeps candidates in proportion to an image's brightness, and Grid samples a field on a regular lattice. Distribution then decides how evenly, from plain Random through Jittered Grid to blue noise, either the strict CPU Poisson Disk or the fast, animation-stable Stable Blue Noise.
Simulate. Particles, sparks, dust and crowds are points the solver pushes around. See Particle Sim and the spawning systems.
Instance and copy. Points are placeholders to put things on. Feed a points cloud and a template into the Iterator and you get one copy of the template at every point, each picking up that point's position, colour and id. See per-element context.
Sample. Read a field's value at each point to colour, size or move it. See Fields & sampling.
The same node covers a single point: leave its input unwired and it emits one, at the position you set.
Sprites
A point can carry a raster as its texture, and then it draws as a small textured quad in the scene. That is a sprite: the value on the wire is points, and the image is an attribute they hold. Thousands of textured points draw as thousands of billboards or cards at little extra cost.
A sprite is textured points. An impostor is a raster holding a 3D look. The two look similar and are different types. See Sprites, impostors & billboards.
Gotchas
A loose points cloud handed to a node that expects a mesh has no surface to work with, so there is nothing to bevel, fill, or shade as a solid. Hover the socket to read what is on the wire, and build or convert to Geometry (meshes) first.
Drive per-point size with @pscale and per-point facing with @orient rather than scaling or rotating the whole cloud. Every instance then varies on its own. Once a transform has been applied to the rows the size moves house: it becomes @scale, a value per axis on the row's placement, and the old @pscale is removed rather than left behind to disagree. Anything asking for one number reads the mean of the three axes.