'Det', 'den' with or without 'där' are 'that'. 'Det', 'den' without anything, like in the given sentence, are 'it'. With adjectives they are 'the'. With 'här' they are 'this'. One could use 'detta' and 'denna' also if one wants to refrain from using 'här'. 'De' is plural, and 'Dessa' is for 'these'. I guess you understand now.