I agree with @krrazypassions that Wikipedia & many free .edu sites offer tutorials as technically deep as desired, usually as measured by how much math is involved. The simplest have none.
@sunssi You said “light reading”, “only the basics,” and “slightly complex.” Do you mean with no math, completely for the layman? That suggests either an entertaining science writer like Bill Bryson (@marinelife‘s answer) or actual eminent physicists who write well for popular readership. Read The Character of Physical Law by Richard Feynman or 1, 2, 3…Infinity by George Gamow. These guys were great writers. Also stuff by Carl Sagan and Isaac Asimov. The list is of course much longer. Oldies but goodies—not necessarily irrelevant by their decades-previous era; in physics you learn the old, then the new. The classics have withstood the test of time.
Since you mention fluid mechanics, a google search of the term plus ”.edu” readily finds a basic online tutorial from Arizona State and a more advanced one from Cal Tech by Kip Thorne (famous physicist) and lots of others. These are .pdf files so I’m not sure those links will work. Some of these might qualify as “slightly complex” or too complex.
Actual books on fluid mechanics are usually expensive textbooks, categorized under “physics” or “engineering.” Check used bookstores or get lucky at a yard sale!