The rules of which materials conduct to which are best learnt by experiment. However, here is a summary for PTCT/NTCT. (Conduction can only occur in the directions indicated by the arrows, e.g. "PSCN <-- NTCT" means NTCT conducts to PSCN, but PSCN does not conduct to NTCT).

At room temperature:
PSCN <-- NTCT <-- NSCN
PSCN <--> PTCT <--> NSCN

When NTCT/PTCT are heated, they swap properties.
"NTCT always conducts when hot (>100C), PTCT always conducts when cold (<100C)".
PSCN <--> hot NTCT <--> NSCN
PSCN <-- hot PTCT <-- NSCN

PTCT and NTCT never conduct directly to each other, or to/from metal. Sparked metal rapidly heats nearby dots of PTCT/NTCT to about 200C. PTCT/NTCT cools to room temperature if left alone.


Therefore:

With intersecting lines of NTCT and PTCT, spark can be transferred from NTCT to PTCT (and prevented from transferring back the other way) by placing a dot of PSCN where they cross.
The same applies for PTCT to NTCT, using a dot of NSCN.


As for the thing further to the right:

The vertical lines of metal heat the dots of NTCT/PTCT next to them when sparked. A spark can only pass all the way through horizontally where the correct lines (and only the correct lines) of metal were sparked. (PTCT - must be unsparked; NTCT - must be sparked). The PSCN is used to connect the NTCT/PTCT and make the hot/cold conduction rule apply. (NSCN could equally well have been used instead).