Thank you, you helped a lot! I thought ROM and kernel was the same

Now I know the diference between unlocking the bootloader, flashing the kernel and flashing the ROM.
Here is what I did with my Xperia Mini ST15i, maybe it would
help some noob like me to do it faster:
1. Unlocked the bootloader
via Sony site. You send IMEI and then you get your unlock code immeditely
2. From freexperia blog
fxpblog.com downloaded CM10, last supported CM for ST15i
3. Installed
flashtool and
flashed kernel (press volume up and connect the phone and PC via USB,LED is blue, run flashtool, flash kernel with boot.img file from CM10 zip)
4. Go in CWM mode (press volume down and power on the phone) and install ROM which you saved earlier on your phone's sdcard
5. Turn on the phone, copy
gapps for CM10 to sdcard and then reboot to CWM and install gapps from zip