follow these steps
1.what is your model???
what ever model you have ...you have to use proper unlock bootloader method for your device.
there are various guides present on this forum for unlocking.
2. after unlocking flash cwm recovery from cm11 thread's first post.(flashing recovery method is also described in unlocking threads)
3. after flashing recovery>>>>download the cm11 from the download link given in the cm11 thread;'s first post.
4. put that zip in your external sd
5. download the quickboot app from playstore
6. open that app>>>click on recovery>>>grant super user permissions(if supersu is downloaded then only....if you only root through towelroot then it does not ask for permission)
7.after phone reboots it will go in cwm recovery.>>>>swipe vertically to go to the menu and right and left for enter and back in the recovery. (or you can use volume buttons for moving up and down and power button to enter)
8. go to wipe factory reset option>>>swipe right to enter>>then click yes
9.then go back to main menu.>>>enter in flash zip menu>>>from there enter in sdcard1 menu>>>drag down to the file you have cm11-xxxxx-nightly.zip>>>press power button to enter or swipe right.>>>again click yes>>>after flash is complete it will say that flashing is complete.
10. go back to main menu>>>and use reboot menu.
and here you are in the cyanogenmod.
i know that it is been repeated N number of times by various people on XDA.
it is standard procedure to flash custom roms.
but when i started first>>>i also have same questions>>>i too was a confused guy about what to do and what not.
so dont get offended...i am just answering the valid question.