Am trying to start mining litecoin with litecoin-qt I have downloaded the litecoin-qt, since I read on a forum, with that I could start mining directly. 
But in my screen, there is not a button for mining.

Have downloaded the cpuminer and have placed the file 'minerd' next to the litecon-qt programm in applications. They are together in one folder. 

Not sure I have understood it well.

Is there someone that could give some ligth on this matter?
Would be very much appreciated.

thnx Adithya!
At some point they removed the GUI for mining from the litecoin-qt client. So you have to run minerd from the command-line or terminal.  The actual command syntax seems to be loosely documented, however. 

Two reasons for this:


cpu mining simply is relatively too slow and unprofitable to warrant much further development. 
Nevertheless the general consensus (at least according to the wiki and other available info) is that pooler/cpuminer is by far a better client in terms of speed, compatibility, usability, etc. 


Also you can pick up a USB ASIC miner for ~$15 (usd) that will far surpass what a CPU can do today. 

As far as the command syntax goes for CPUminer check out
https://bitcointalk.org/index.php?topic=55038.0

And scroll down to basic usage examples. Also may want to register at a pool first and have your login details ready.