Beginner PHP function questions

Hi guys,

I am trying to understand these questions regarding function and how or where can i get some knowledge to understand and create the code.

questions are:
1. Open the text file “status.txt” as read only using variable $handle to store the file handle.
2. Begin a session.    (what does it mean begin session? does it mean start using the if condition?)
3. Return the number of elements in array $days. 
4. Convert an array $data with five elements into a string that is delimited by tab.
 (what does it mean by delimited by tab?)
5. Check if the form text item "status" obtained via get method is empty.

Thank you in advance!