The kits are main powered and use potentially lethal voltages. Under no circumstance should someone undertake the realisation of a kit unless he has full knowledge about safely handling main powered devices. Always work on a clean and tidy area. Always pull off the mains plug before working. Turning off a switch is not enough.
What skills are needed ?
Meticulous care is the first skill you will need to build one of those kits. One single component that is not in the right place , in the right direction, one single solder joint that is deficient and the whole thing won't work ! So the secret to success is simple : follow the assembly guide down to the letter and triple check all your moves.
Good soldering practice is also needed. Your boards will be as weak as your weakest solder joint. So this is very important. But easy to learn. If you have no soldering experience, start practising with a piece of Veroboard and a handful of resistors. You should be perfectly operational after one hour or two.
Basic electrical and electronic understanding. Do you know what is a Volt, an Ohm, an Ampere ? Can you use a digital multimeter ? These are the questions you must ask yourself. If the answers are no, you might try to find a friend that knows or buy an assembled kit.
If you own these 3 skills, your kit will work first time.
What tools do you need ?
A good soldering iron, preferably thermally regulated, 60W, with a medium size tip (1.5-2.5mm wide), screwdriver shape.
Solder. Only use first grade solder, 0.7 to 1mm diameter, "no clean" type. Good quality solder will make the soldering process easier and you will get nice shiny joints.
Cutters. If you plan to go ahead with DIY, buy good quality cutters.