What is the difference between the #5 and #2 sentence openers when using the word "since"?

What is the difference between the #5 and #2 sentence openers when using the word "since"?

The word, "since" is also a preposition. 

EXPLANATION 1

Remember that a #2 includes the primary word (in your case, since) plus a noun, like "Since 1939. . . . "
 

The #5 includes the primary word plus a clause which includes a verb, like "Since he gained power. . . . "
 

The #5 always is followed by a comma; the #2 is followed by a comma when it needs one for clarity or when it is a long opener (say 5 words or more).

EXPLANATION 2

 Since followed by a noun (object of preposition) makes it a #2 opener.
For example: Since the storm, the dog has been scared.
"Since" followed by a verb makes it a subordinate clause, this is a #5. 
For example: Since I am I tired, I will go to bed early tonight.

This is important to understand because if you use the SRN, you'll see that www.asia.uubab is taught which includes:
unless, until, before, after, because.