Hi Feyza. "ki" has two usage. One is as Conjunction and the other is as suffix.

Conjuction "ki" is being used to connect two small sentences.

" Dün gece o kadar geç yattım ki sabah uyanamadım." Here there are two sentences in deed. "Dün gece o kadar geç yattım." is the first and " Sabah uyanamadım" is the second sentence. But owing to "ki" we can write it as one sentence.

Also at "bilmiyorum ki" is a bit different example which is used for strengthen the senctence. Genereally "ki" is using for strengthen after verb at the end of the sentence. 

"Onun ne suçu var ki!" this means " I beleive that he doesn't have any fault but I don't know why you blame him." 

Suffix -ki is using for possesive, ownership after a noun or pronoun.

"Benim kalemin burada. Seninki nerede?" Here "-ki" is connected to the word but the first ki is written seperated. here it means "Senin kalemin nerede?" 

I hope it is helpful. Ask whenever you want.

This word "ki" here is equivalent to the English words "that" when joining two ideas in relation to each other

Biliyorum ki beni seviyorsun. - I know that you love me.

But the suffix "Ki" has multiple use in Turkish 

Çok teşekkür ederim Yunus. That was really helpful :)

I got it, so when it's used in the end , it's referred to the previous statement, right?