Can I improve my skill just by using it?
I know, I can impove it by training.
But when I will mostly use the KICK, wil this skill be improved too?

So, you'll have to practice the skill to get it to some useful level. If the skill is at 1%, it does not improve. You cannot practice a skill above 75%, as the rest of the skill % must be gained through use. The skill % has a chance of improve when you are using it. The specifics on the chance for improvement are explained in the helpfile of skill improvement.

Short answer is: if you have practiced kick above 1%, it will improve in use.

The general guideline for practicing is to wear +int gear to max your int when you use practice to a skill. If you have 23 int or above, 1 practice/skill is enough(1 prac practices it to 71% at int 23. It'd be waste of practice to put a prac in that 4%). If your race isn't smart enough to get 23 int or above, You should have at least 17 int, so that 2 practices is enough to practice the skill to 75%.

Thank you, it is exactly I wanted to know.

Help Skill Improvement details most of the important aspects to this, but the short answer is yes.