Hi and thanx for your help in advance

in this sentence

Osmanlı Devleti´nin ilk zamanlarında (kullanılan) gümüş akçe vardı.

the suffix (lan) what does it mean and when do we use it and thank you

"There was a silver coin which had been used in the early days of the Ottoman Empire."

kullan|ıl|an = VERB STEM + PASSIVE + PARTICIPLE

O akçe Osmanlı Devleti´nin ilk zamanlarında kullanıldı. ´it was used´

akçe is the grammatical subject of this passive sentence > the participle modifying it must be of the -(Y)EN type.

first of all thank you for your answer it really helped

and can I know where I can find the use of these (participles) and why do we use them?

In Turkish, there are no subclauses as we understand them. When we want to embed a sentence into another sentence  -  make a complete sentence a constituent of another sentence  -  the verb of the embedded sentence often takes the participle form. For instance in reported speech, equivalents of the English relative clauses, indirect questions and certain adverbial clauses participles are used.

It is a big question, learn it piece by piece. Click the Participles headline at www.turkishlanguage.co.uk and you can get a basic idea and find plenty of examples.

 I really appreciate your help thank you again