What is Tostring and To list

I am new in Programmming ..   I saw in one page some code like below  GridView1.DataSource = query.ToList GridView1.DataBind()
Also Where p.StudentID = Session("StudentID").ToString

  i could nt get it what  is  TO String and To list  .. Some one please explain me the differnce  ... Also what is string actually means .. 


thank you  
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