I´m having some difficulties with demonstrative pronouns. 

When should I use bunum/şunum... and when should I use Bu/şu...? and what are the grammar rules exactly?

Thanks in advance  

Bunum/şunum?! What are those? I never use bunum/şunum. Sounds like "my this/my that" but I never use it.

lol yeah i didnt understand it either, that´s why i had some difficulties.. but that´s what i found in some lessons. what should I add when I use Bu/Şu...? 

http://www.turkishclass.com/turkish_lesson_29

 you´ll find it here on this page, scroll down to demonstrative posessive pronouns  

Hmm... On that page it says "bunuN/şunuN". One letter, huge difference.

bu / şu can be used on their own, without adding anything. You don´t have to add anything.

bu - şu means this - that. I can´t think of a counterexample to bu=this/these and şu=that/those.

Bunun-Şunun means "of this" "of that". This may change though, depending on where they´re used.

I know I don´t add much to what´s written on that page but there´s really not much to add.

Thanks a lot  

So i just use Bu and the word without adding anything to it

example: Bu bir kalem

             Şu bir masa. 

What if I want to say "This is my pen"

I say: "Bu benim kalem" ?  Is it correct? 

http://www.turkishclass.com/turkish_lesson_257 (the last part of here is about genitive case)

http://www.turkishclass.com/turkish_lesson_274 (here is about "bu, şu, o".)

And I should also give the combinative letters: http://www.turkishclass.com/turkish_lesson_254

The genitive is "-in". If the word that you add the genitive suffix is ending with a vowel, the combinative letters is "n".

bu+in(genitive)-------------------->bu+un[vowel harmonies require this] ---------->bunun (of this)

-in must turn -un because "u" (bu) is hard (in aspect of major vowel harmony) and round (in aspect of minor vowel harmony)

o+in(genitive)--------------------->o+un--->onun (1his, her, its, 2of that, of it)

Bunun rengi daha güzel. (The colour of this one is nicer.)

Onun ayağı sakat. (His/her foot is injured.)

Elindeki parça bunun. (The fragment on your hand belongs to this. (purely: ...of this))

renk (colour)

yara, sakatlık (injury)

sakat, yaralı (injured)

Öz saygı çok önemli. Bunun önemi özellikle üniversite yıllarında açıkça anlaşılır. (The self esteem is very imporant. One clearly understands the importance of this especailly in university years.)

bunun önemi

öz saygı (self esteem)

çok (1much, 2very, 3many)

önem (importance)

özellikle (especially)

açıkça (clearly)

Thanks a lot