When trying to go about meditating for the first time, often you will have a very difficult time trying to calm your mind. No one is expecting to you to reach a state of enlightenment or become the next Buddha, only be consistent.
What works for me is waking up 30 minutes earlier than when I would normally wake up. I know for these thirty minutes I do not have anywhere to be and it is early in the morning so I will not be interrupted. Pick a time that works for you and stick with it.
As far as being able to sit for extended periods of time, find some meditation techniques that interest you and try them out; you're in what I like to call your trial and error period until you find something that works for you. I personally go for breathing techniques that help release tension and slow the heart rate down. When my mind starts to shift, I focus on my breathing. Become aware of your body, feel the air entering through your nose, imagine the path it takes through your body; feel your heart beat, imagine your blood flowing to each limb.
When I first started, I could barely sit for five minutes. That's perfectly normal, just stick with it. Eventually you'll find yourself able to take a step back from your mind and just watch your thoughts flow like movie reel.
Also, the day you don't feel like meditating, is the most important day to meditate.