A complete skateboard is pre-assembled - it almost rides right out of the package and on to the streets, ready for you to practice all your new tricks. You simply don’t have to think about buying the separate parts like trucks, wheels, decks or the likes. Once you have gained more experience on the board and you feel like customizing it to fit your skateboarding style, you can begin to learn more about the different pieces in order to assemble a skateboard that meets your specific wishes and demands. Until then, a complete can be quite the right choice.
To summarize, a skateboarder's feet need to do two things successfully to complete an ollie. They need to provide a changing force to move the board correctly (so that the combined force of gravity and the skater's feet add up to the green arrows above), and they need to provide different amounts of force with each foot (shown by the red and blue arrows above) to steer and turn the board into the right orientation.
Smile and wave – Feel free to look around at all the other people at the skatepark that stood by and marveled at your new-found accomplishments (all one of them). I’m sure by this point you’ll be picking up roses that are being thrown at your feet, and taking a well-deserved bow as they begin to chant your name. Take it all in, thank the crowd for their undying affection, and then go get a snow-cone. You deserve it, champ.