FAQ: How to use a function properly?

I have seen many people using a function incorrectly so thought of referring this question for the future purposes instead of starting from the beginning. Hoping that many advices are shared here..

[Jan]

I do not understand the question. Who did use which function incorrectly?

[madhan ravi]

I mean some users who ask question . I want this thread to be a guide for the correct usage of function.

[Bruno Luong]

Those users are simply lazy to read the doc and take a short cut jumping straight a head with out playing with function calling.

They won't read this thread.

[madhan ravi]

HaHa true .. just a try..