I am working on an exercise and the following sentences have come up

Yuzen var mi?

Ziplayan var mi?

Telefonda konusan...

I don´t recognise the tense or ending. Maybe I have yet to cover this.

Can anyone help?

That´s the pasive voice of Turkish.
You have so much more about it here: 
 http://www.turkishlanguage.co.uk/passivemood.htm

You have come across with your first active participles, Johnk. There meaning is as follows:

yüz|en adam ´the man who is swimming/swims/swam/...´

zıpla|y|an çocuk ´the child who is jumping/jumps/jumped/...´

telefonda konuş|an bayan ´the woman who is talking/talks/was talking/... in the phone´

This verb form does not give any hint about the tense but follows the timing of the main clause predicate. That is why I gave more than one alternative for the translation.

Your exercise makes me wonder. Turkish adjectives may quite freely function as nouns also but if I was to explain this grammar point I would start with the adjective function. Anyway, Yüzen var mı? ´Is there (someone) who swims?´

For a clearer explanation and plenty of examples look here:

http://www.turkishlanguage.co.uk/subpart.htm

OK I will try to explain, as I have recently covered this topic in my Turkish classes. I will try to go step by step.

In Turkish there are ´relative clauses´ which work like simple adjectives to describe a noun. Depending on whether the noun is the subject or object of the sentence, (and also the tense) will determine which ´subordinating suffix´ you can use. 

That man was running. Who is that man?

In English we can simplify the 2 sentences into one sentence, because the subject is the same in both sentences.

Who is that running man?

In Turkish you can do the same using (y)en/an suffix attached to the verb root.

Koşmak = to run, koşan adam = running man

Bu koşan adam kim? Who is that running man? 

or to put it into slightly better English, Who is that man who was running? 

Hopefully that part makes sense to you.

Turks can further simplify these types of sentences where general terms are used for the noun, like ´person, thing´ by dropping the noun from the sentence.

The translation for ´Who is the one (person) who is running?´ becomes

Koşan kim?

Now we can get back to your examples, and let´s correct the spelling as well

Yüzmek = to swim. Yüzen (kişi) = one who swims

Yüzen var mı? = Is there anybody who swims?

Çay isteyen var mı? = Is there anyone who wants tea? 

Later you will come across other versions using diği and (y)eceği where a sentence has different subjects but the same object. 

Sorry Abla and nemansjasrb, I was still working on my answer when you posted yours. Anyway, the more explanations the better (as long as they are correct)

You explained it excellent! Thank´s a lot.

I just had to answer this as I have just been explaining to my husband about how we use the words drift and drifter. As the previous replys have explained the ending indicates it is the person performing the action, so I have put it into the context I have just been discussing. Hope it helps