Your first picture

In pic you describe a drawing and the language lays it out: you imagine walking across the page dropping primitives, and everything chains from the current position and direction.

.PS
ellipse "document"
arrow
box "rpic"
arrow
ellipse "SVG"
.PE

Each object places itself after the previous one; arrow moves the current point. No coordinates needed — but they exist when you want them.

Naming and anchors

.PS
A: box "parser"
B: circle "IR" at A.e + (1.2, 0)
arrow from A.e to B.w
box "backend" with .w at B.e + (0.4, 0)
.PE

Labels (A:) name objects; every object exposes compass anchors (.n .ne .e … .c .start .end) you can position against.

Where to go next

• The language tour covers primitives, attributes and macros.
• The extensions chapter documents everything rpic adds beyond classic pic — each one opt-in, from gradient fills to texlabels TeX math.