There are a lot of areas where those kicks need work.
Firstly, you're not planting your lead foot. Its sliding around and making your kicks (which need work) worse because you can't drill them in, and it makes you look sloppy. Go through the kicking motion slowly, and repeatedly. Focus not on the kick itself, but shifting your weight onto one leg and not sliding around with that leg. Also: lose the socks. they ruin traction and make an injury a much more likely scenario.
The kick itself is really in need of work. You're not drilling the kick in it seemed like. More just slapping the bag with your shin/instep. Work with low kicks or body kicks at the most to make sure you can drive the shin bone into the bag with power AND technique. Watch demo videos on youtube to make sure you're getting the technique as exact as possible.
The rest of the body: During the kick, your body mechanics are all off. It looked as though you were tensing up before throwing the kick. Don't do that. Throwing a kick with any kind of power is a fluid movement. Hip rotation, core rotation, the snap of the leg. Its something that comes with time.
Work it slowly and repeatedly and watch your core, hips and legs move. The best way to become good at a technique is to understand how the technique works. Over time as you keep throwing the kicks they'll become more fluidic and powerful.
People will always tell you to get into a gym or your shit. But frankly, unless you're going to compete in MMA in the next six months to a year, its a waste of money. Basic combative skills do not require a coach, the first man to throw a punch didn't need someone to show him, the first man to block a punch didn't need someone to show him how.
Sig courtesy of that photo-matic magician limba
I went out the way that I fight. I went out on my shield. Thatís it. Done. --Chuck Liddell
My goal is to end my opponent --Carlos Condit