I have read this, but it still hasn’t filled my brain yet. When I play chess, sometimes I'm often laughing and putting some pressure on my opponent. Is it forbidden in legal game? Is there a rule about it?
The FIDE Laws of Chess:
11.5 It is forbidden to distract or annoy the opponent in any manner whatsoever. This includes unreasonable claims, unreasonable offers of a draw or the introduction of a source of noise into the playing area.
Distracting or annoying the opponent in any manner (other than making good moves!) is forbidden, and making noise is forbidden. So laughing in order to give pressure to your opponent is forbidden.