This and That

 "This" is questo before a masculine noun and  questa  before a feminine noun:

questo libro       this book

questa strada    this street

 "These" is questi  before a masculine noun and  queste  before a feminine noun:

questi libri         these books

questa strada    these streets

 "That" is quel before most masculine nouns, quello before masculine nouns beginning with "z" or "s" plus another consonant, quella before most feminine nouns and quell' before all nouns beginnning with a vowel:

quel libro            that book

quello studente  that student

quella casa          that house

quell' albero        that tree

quell' arancia       that orange

 The plural "those" is quei  before most masculine nouns, quegli before masculine nouns beginning with "z" or "s" plus another consonant and before masculine nouns beginning with a vowel, and quelle before all feminine nouns:

quei ragazzi        those boys

quegli stivali       those boots

quegli alberi       those trees

quelle case         those houses