What is Influence in Sociology?

[Hevan]

In terms of Social life in Internet, I am on the lookout for explanation of Influence and how many different ways it can be done.

In university, I took only one course related with Sociology, others all based on Computer Science. Thus, the question may be simple enough not to answer for you, but I, even, do not guess where to look to find answers.

I am looking for answer to ;

• In Social web, how does accounts influence each others?
• In Social web, what makes account as counted as influencial?
• In Social web, what makes influence counted as weak or strong?

(It is also welcome to share link(s) to survey, book, or web site.)