Did your hydrometer come packaged in a tube that was 2 to 3 inches longer than the hydrometer? If it did you will use that tube for your wort sample to float the hydrometer in. Homebrew shops usually sell these tubes, but any type of clear cylinder will work that is not overly large. Do not put your drawn sample back in the fermenter. This risks infection. I always drink it to track the taste as fermentation comes to completion. I would recommend buying "The Joy of Homebrewing". This will answer many questions and fill in the blanks found with recipe instructions. Very easy to read book.