citet{X}  gives "Jones et al. (1990)"
citep{X}  gives  " (Jones et al. 1990) "

multiple:
citet{X,Y}
citep{X,Y}

see, for example, amoung others:
citep[see][chapter 2]{X}

all authors:
citet*{X}
citep*{X}

suppressed parenthese:
citealt{X}
citealp{X}

no data:
citeauthor{X}

forced uppercase (del Rossa):
Citep{}

aliases:
\defcitealias{X}{PaperIII}
\citetalias{X}
\citepalias{X}