When do we say Al Hanissim
Al Hanissim is said on Chanukah and Purim in prayer and in Birkat Hamazon. The siddur has separate pages for each. On Chanukah we say the Chanukah version, and on Purim the Purim version. The insert appears in prayer and in Birkat Hamazon on those days. You can open the dedicated siddur pages, or Birkat Hamazon with the holiday marked.
Is there a Purim page?
Yes. The siddur has a separate Purim Al Hanissim page.