There are a number of ways to elevate your base cabinet to allow for a recessed toe-kick area. Some cabinetmakers build the tor-kick integral with the cabinet box. I prefer to build a simple box and then elevate it in one of two ways.
The first way is to use scrap plywood and simply build a base platform, usually about 4 inches tall and to a depth of four inches less then the depth of the cabinet. The base is constructed in a manner similar to the way a wall is framed on the floor before it is erected. But instead of studs that are 8 feet you are using plywood “studs” 18 inches or so in length. Once the platform is built, it is shimmed level, and screwed to the wall. The cabinet boxes are then placed on top of this level base or platform.
A second method that is popular is to use adjustable feet. This method is used in frameless cabinet construction and is easy to makes leveling your cabinets a breeze. The cabinet bottoms do have holes bored in them at the proper location, in order to mount the adjustable feet. There are several manufacturers of adjustable feet; my advice is to not select based solely on price. Even the pricier feet are cheap when considering the cost of the job, and they will make installation much easier.
There are a number of ways to level cabinet bases. The two described above are my two favorites, and in my opinion are the easiest to implement.