I'm learning PHP.
While learning PHP, I noticed that there are few entities in PHP which are used in different fashion. Sometimes with the pair of parenthesis with the enclosing parameter/s between them, sometimes with the pair of blank parenthesis(i.e. without any parameter/s or message/s passed) and sometimes without using a pair of parenthesis.
How could this be possible? Is it possible for all other entities(i.e. functions / keywords / language constructs) also that are present in PHP?
Are there any other such entities present in PHP other than 'echo', 'print', 'die', 'exit' which I come across till now?
What these entities actually are called functions / keywords / language constructs in PHP?
What's the correct method / way / coding standard to access such type of entities?
It would be better for me as well as other PHP community members who are trying to learn PHP if someone could answer all of my queries in a simple, lucid and easy to understand language with the reliable explanation?
Thank You.