This time I read the guide on ConTeXt Wiki and learned some basic commands doing quotation.
Not very much today in fact.
1.single quotes (‘):

\quote{some text}

2.double quotes (“):

\quotation{some text}

3.long quote sections:
For single quote:

\startquote ... \stopquote

For double quotes:

\startquotation ... \stopquotation

4.Nested quotations:
Add following lines first:

\setupdelimitedtext
  [quotation]
  [1]
  [left={\symbol[leftquotation]},
   right={\symbol[rightquotation]}]
 
\setupdelimitedtext
  [quotation]
  [2]
  [left={\symbol[leftquote]},
   right={\symbol[rightquote]}]
 
\setupdelimitedtext
  [quotation]
  [3]
  [left={\symbol[leftquotation]},
   right={\symbol[rightquotation]}]

Then try with:

\starttext
Testing, \quotation{A long quotation in which one character says,
\quotation{Eh? What am I supposed to say? Something like, \quotation
{Quotations in this sentence are nested}?}} testing, 1, 2, 3.
\stoptext