a question about oddities in the data directory

Apologies if I asked this question before.

I’m a newcomer to Postgres, having migrated from Mysql.  Information about tables seems harder to get at in Postgres.
Thatdata directory on my machine is suspiciously large—well over 100 GB.  The directory Postgres/var-9.5/base/ contains
anumber of subdirectories with Arabic numerals. Directory 16385 has a subdirectory 17463 with a size of 1.07 GB. But
thereare also 17 subdirectories with names from 17463.1 to 17.463.17.  There are also other entries with similar forms
ofduplication and suspiciously identical file sizes of 1.07GB.
 

Is this normal behavior?  Where in the postgres documentation do I read up on this? Postgres strikes me as superior to
MySQl,especially with regard to string functions and regular expressions, but it’s harder to look under the hood. How,
forinstance, do I figure out what number corresponds to the table that I know as ‘earlyprinttuples
 

With thanks in advance for any advice

Martin Mueller
Professor emeritus of English and Classics