One of the features that makes Craft Warriors unique is that you are able to 'craft' your own characters. This basically means you can customise how the character looks by building your own skins from scratch. This feature is purely cosmetic and does not impact gameplay in any way.
To customise your units you must do the following:
1) Go to the 'Units' tab.
2) Double tap on a unit you want to customise.
3) Tap on the pencil icon at the top-right of the pop-up window.
4) Start editing and save.
If artistic talent is not your thing or you don't have the patience there is always the option of using what other players have created by going to the Market and selecting the 'Skins' category and browsing through the different skins until you find one you like. Then it's just a case of tapping on the skin you want and choosing 'Download'.
Once the download has completed you need to unlock the skin for use. In order to do this you tap on 'Add Craft Model'. Now go to your barracks, select the unit that you want to use the new skin and tap onthe blue icon on the lower right of the screen and choose the new skin.