Q:

I am famous, I am in maths , I am the sun. What am I?

This is my first question, so feel free to edit. I am open to suggestions.

Oh! I am so excited!! This is my first puzzle!
  I can show you where the things are. Ready for a quick game?
  I am rich you know! I can be usually in a command, or a hat.
  And...
  I am famous; I am in maths; I am the sun.
  Open me... close me, you will get less or more.
  Guessed it yet? I think it's worth trying for!

Each line represents something. Combining all those things gives you the answer. But the final line is just for the rhyme (I know it's not a good one, but I tried).
Hint:

 It is related to something, every member on every Stack Exchange site uses.

A:

This seems to be related to

 the symbols on the number keys of a computer keyboard, read left to right. I initially thought each line referred to one key, but now I think each symbolizes a block of consecutive keys.

Oh! I am so excited!! This is my first puzzle!

 Exclamation mark '!'

I can show you where the things are. Ready for a quick game?

 At-sign '@' (on US keyboards) followed by '#' perhaps symbolic of tic-tac-toe (thanks to user IdiotStyle for this suggestion). Or maybe '@' is for the game Nethack, but that's not quick unless the player is unlucky or careless.

I am rich you know! I can be usually in a command, or a hat.

 Dollar sign $ symbolizing money, followed by '%' used for variable substitution in MS-DOS/Windows commands, followed by '^' (informally called a hat). Or maybe they're all $ (rich: obvious; command: Unix shell command prompts; hats full of money are a bit of a cliche).

And...

 Ampersand '&'

I am famous, I am in maths , I am the sun.

 Star (asterisk) '*'

Open me... close me, you will get less or more

 Parentheses '(' and ')' followed by '-' and '+' (we're now no longer on the number keys, but still on the same row of the keyboard).

(Thanks to user IdiotStyle for proposing some improvements used above.)

A:

Main credits go to Gareth McCaughan for his answers put me on the right track.
It is:

Indeed the symbols on the top row of a keyboard from left to right

Oh! I am so excited!! This is my first puzzle!

This is an exclamation mark '!' as the leftmost symbol. (1)

I can show you where the things are. 

The things are "at" '@' (2)

Ready for a quick game?

The hashtag '#' is also the playboard for a quick game of Tic Tac Toe. (3)

I am rich you know! 

The Dollar sign "$"(4)

I can be usually in a command 

The percentile symbol '%' (5)

or a hat.

The hat symbol '^' (6)

And...

The sign for "and", the ampersand '&' (7)

I am famous, I am in maths , I am the sun.

A Star is famous, in math the asterisk is a multiplier symbol and the sun is a star. '*' (8)

Open me... 

Opening parenthesis '(' (9)

close me, 

Closing parenthesis ')' (0)

you will get less 

Minus sign '-' (-)

or more

Plus sign '+'

