1-Why sometimes( Unuttuğun ) written a that way and some times it is written (unuttun)?

2- what is the different between (yüzlüm) and( yüzü)?

3-what is the meaning of the suffixes (sel)( sal)?

4-What is the letter (şrefer to in (anlaştık)?

5-What is the different between (yorldum)(yorgunum)(zorladım)(zorudayım)?

--Thanks in advance and sorry for too much questions--

unuttun is a simple verb form. You just split it into pieces and analyse unut|tu|n = ´forget´ + PAST + sg 2nd > ´you forgot´.

Sometimes and not seldom sentences become parts of other sentences. We call them subclauses or embedded sentences. This process causes some changes in the embedded sentence, the most important being adding the subordinating suffix -DIK- to the verb. -DIK- shows that from now on this is not a verb but more like a noun or and adjective. Thus, it does not take tense markings or personal endings any more but possessive suffixes and case endings.

In unut|tuğ|un I presume you understand -tuğ- stands for -DIK- as one of its many forms. -un is a possessive suffix for sg 2nd.

Two sentences about the same wallet:

                   Cüzdanını unuttun. ´You forgot your wallet.´

                   Cüzdanını masaya koydum. ´I put your wallet on the table.´

Let´s embed the first sentence into the second one. Look what happens to unuttun when we subordinate it:

                    Unuttuğun cüzdanını masaya koydum.

                    ´I put your wallet  -  which you forgot  -  on the table.´           

3-what is the meaning of the suffixes (sel)( sal)?

This suffix generally comes to the nouns and alters them into adjective.

duygu --> Emotion 

duygusal ---> Emotional

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kişi ----> person

kişisel ----> personal

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gelenek ---> tradition ,custom

geleneksel ---> traditional, customary

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tarih  ----> history

tarihsel ---> historic

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ulus  ---> nation

ulusal ---> national

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bölge ----> region

bölgesel ---> regional

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However, This suffix comes onto two verbs which are exceptions.

işitmek----> to hear

işitsel-----> audial

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görmek  ----> to see

görsel   -----> visual

My attempt to explain this ....

 The adding of (vowel)ş to some verbs means the action occurs with each other

For example

anlamak (to understand) anlaşmak (to understand each other)

sevmek (to love) sevişmek (to love each other)

görmek (to see) görüşmek (to see each other)

benzemek (to resemble/look like) benzeşmek (to resemble/look like each other)

ağlamak (to cry) ağlaşmak (to cry together/with each other)

tanımak (to be acquainted with) tanışmak (to be acquainted with each other)

bilmek (to know) bilişmek (to know each other)

I´d like to add bit more onto Henry´s good explanation.

Reciprocal Verbs

This type of verbs are formed by adding -ş [ -ış, -iş, -uş, -üş ]

Verb stem  + -ş [ -ış, -iş, -uş, -üş ] + tense ending + Personal marking

anla      +       ş              +                     dı            +        k

anlaştık ----> we agreed , we compromised.

as you see, the verb anlamak [to understand] changes into another verb anlaşmak [to agree on something] , literally, we understand eachother, we found a way by understanding eachother and we came to an agreement on something.

The action is performed together by more than one person.

The action "anlaşmak" in our case is performed together.

The action is performed by a group of people or non-human.

uçmak - to fly

uçuşmak -  to fly together [birds...etc]

Kuşlar o yöne doğru uçuştular

The birds flew towards that direction.

The action ´fly´ is performed by a group of birds.

The action is performed by [to] eachother.

yazmak --> to write

yazışmak ---> to write [to] eachother

 [Biz] Arada sırada  yazışırız.

Time to time we write [to] eachother.

2- what is the different between (yüzlüm) and( yüzü)?

Yüz + lü [with] + m  ---> literally, with my face but in the context;

 Güzel yüzlüm   literally; my with beautiful face ---> My beautiful faced

 When you adress your lover to say my beautiful faced darling.

 Benim güzel yüzlü yarim --> My beautiful faced darling.

 Güzel yüzlüm ---> [My] beautiful faced [darling]

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Yüz - face

Yüz + ü ---> in possesive form ; his,her,its face

Onun yüzü --->  her face

Onun yüzü çok güzel ---> her face is very beautiful

Thanks so much for all

This is how I understand the difference as a learner.

Yorgun is an adjective which means tired, weary, fatigued.

You can add a personal ending to get a nominal sentence (ad tümcesi)

Yorgunum = I´m tired. Yorgun değilim = I´m not tired.

Nasılsınız? (How are you?) Yorgunum (I´m tired)

Yormak is a verb which means to tire.

Yorulmak is a passive verb which means to get/become tired.

Yoruldum = I got tired, I became tired, I´m tired of .....

Generally a reason, cause or explanation will be given before yoruldum is used.

Söylediklerini duymaktan yoruldum. = I got tired of hearing what you´re saying.

Zorlamak is a verb

zorla + dı +m (past tense, 1st person) = I forced ..., I put pressure on

Zorunda is used with verbs to express necessity/obligation

Burada kalmak zorundayım = I have to stay here

Necessity can be expressed in many ways in Turkish

-meli + personal markers

-mek/mesi gerek/lazım/gerek-

-mek zorunda/durumunda ol-