Hi I just read some sentences that have some suffixes I´m not used to. In the following you will find these sentences:

O çorabını giyiyor. (suffix: ın )

O ayakkabısını giyiyor. (suffix: sın)

O gömleğini giyiyor.  (suffix: in)

O pantalonunu giyiyor. (suffix: un)

What I wanted to know what´s the use of these suffixes and when I should use them or is it only for harmony.

Thanks

They are possesive suffixes.

He is wearing his sock(s).

additional info:

He is wearing the socks.

O, çorabı giyiyor. (If you mean he is doing the action now)

He is wearing socks.

O, çorap giyiyor. (If you mean he has some socks on)

Teşekkürler

 I don´t know what made you think they were, but ın, sın, in, un are not suffixes here.

Possessive suffixes for 3rd person singular are: -ı, -i, -u, -ü; -sı, -si, -su, -sü.

çorap - çorab-ı

ayakkabı - ayakkabı-sı

gömlek - gömleğ-i

pantolon - pantolon-u  

Between 3rd person´s possessive suffix ending in a vowel and a case suffix there always is helping sound -n- :

In the examples the case suffixes are -ı, -i, -u, (-ü  as the words are direct object:

çorab-ı-n-ı

ayakkabı-sı-n-ı

gömleğ-i-n-i

pantolon-u-n-u

There is a similar thread here.

Teşekkürler herkese

Another one is coming here execuse me but I just have no clue what´s it for

Bunlar gerçek çiçektir

I know that it´s originally dir but what´s the -dir suffix is for?

The ´dir´ suffix is often used in official notices or newspapers and has a similar meaning to ´is´ or ´are´. It also has other uses as a suffix, but in your sentence it means ´are´. 

Bunlar gerçek çiçektir = These are real flowers.

See this link for more discussion about this suffix.

I think it is not used much in spoken Turkish, unless wanting to stress a fact.

Another link to explain it more.

Herkese Teşekkürler

another suffix I´ve found in homework here

kaldık-görmedik (dik)

I know di is for past tense and then we add the suffix for each pronoun

also another suffix I found on a poem:

isteyipte (ip)

´kaldık´ = ´we stayed´ and  ´görmedik´ = ´we saw´.  ´Dık/dik´ here is the first person plural ending not a suffix.

The ´ip´ suffix is used to join two verbs instead of using ´and´.  

Example: ´Bu akşam banyo yapacağım ve saçlarımı yıkayacağım´(This evening I am going to have a bath and I am going to wash my hair) becomes 

´Bu akşam banyo yapıp saçlarımı yıkayacağım´ (This evening I am going to have a bath and wash my hair´ - both meaning exactly the same thing.

The tense of the first verb is determined by the tense of the second verb.

More about ´ip´ here.  [not too sure about the ´te´ ending on ´isteyip´ though  ]

Isn´t görmedik we didn´t see?