Copying code from an example is a very important first step. Often, you will want to copy someone else's program you find on the internet and then modify to meet your needs. 

When you are first starting with programming or a new language, you do not need to understand everything that a program is doing. Simply knowing where to look to make your changes is enough.

Can you change the Blink program from the last lecture so that LED 13 blinks on for 0.25 seconds and off for 0.25 seconds?

When you upload your program to the Arduino, the LED attached to pin 13 should blink much more quickly.