GPIO command and parameters

The link given in DOCs is not working and i am unable to understand the GPIO commands like digitalwrite digitalread etc. So help me to understand all the GPIO commands of and their parameters

here,GPIO: General Purpose Input Output ,first we are using this for functioning digital signals;
coming to your question first "digitalread"means it reads the digital signals form the component ,as “digitalwrite” it writes the value gained by digitalread ie.)if you are connecting your LED to indicate something when it turns on the digitalread only reads the value of the LED then digitalwrite writes the status in the serial port; in this case digitalread and digitalwrite is used because the component is digital component.In case of analog device we must use analogread and analogwrite to perform the tasks

Sharing the link. Might be useful for better understanding and explanation.