Buying skills

How to make buyable skill, I mean hero can buy it a shop and it will level-up when bought next time?

Well, in the trigger editor there are options for all that. You could just make the shop buy units then you could remove the unit and do the proper actions on the hero. You could also do the same with items, but it wouldn't work if your inventory is full.

Also I like the icons in your signiture how could I get the files to possibly use them?

With triggers ofc..If i were you, i would put tomes as 'skills' so that u dont have to remoe anything, and u can make them give no stats in object editor easily. Then u trigger them so that hero learns skill if he buys specific tome :)

In more detail:

In the object editor find, copy/paste, and edit a tome to give nothing and use the proper abilities icon. Add the tome to a item shop (magic vault, etc).

In the object editor again, whatever hero your using, add every ability (the real ones) to the hero.

In the trigger editor, at the start of the map disable all the abilities. Now, when ever a hero buys a tome-ability which if it already has the ability and if it does level is up by one, otherwise enable the ability and set its level to one.

I think that should cover it.