Pullup and Pulldown resistors?

Can someone explain this to me? Like link a website or something which will help me? I am trying to wire up EKMC1601111. Any help would be greatly appreciated!

Datasheet: http://elcodis.com/parts/2241625/EKMC1601111.html#datasheet

lets say you want to put a switch on a digital input. you connect one side of the switch to ground and the other side to the digital input. when the switch is closed the input is connected to ground, but when it is open the input is connected to nothing (it is floating). this is bad because inputs are made to be high or low not somewhere in between. so if you now put a ‘pull up resistor’ between the positive supply and the junction of the switch and digital input the input is pulled up to an unambigious high when the switch is open. a pull down resistor connected to ground would do the same for a switch connected to the positive supply and the input.

lets say you want to put a switch on a digital input. you connect one side of the switch to ground and the other side to the digital input. when the switch is closed the input is connected to ground, but when it is open the input is connected to nothing (it is floating). this is bad because inputs are made to be high or low not somewhere in between. so if you now put a 'pull up resistor' between the positive supply and the junction of the switch and digital input the input is pulled up to an unambigious high when the switch is open. a pull down resistor connected to ground would do the same for a switch connected to the positive supply and the input.

Just wondering, would you need to do this for buttons too?

if the button is a momentary switch, yes.