Learn Hardcore Russian: На конференции есть секция по биологии. - At the conference there is a section on biology.

Russian usually uses на with events and activities (conferences, concerts, exhibitions, lessons, meetings), because they are seen as occasions, not physical containers.

You normally say:

на конференции – at the conference
на уроке – in class / at the lesson
на концерте – at the concert
на выставке – at the exhibition

Using в конференции would sound wrong in this context. В is used more with physical spaces and enclosed locations (in a house, in a city, in a room).

Why does конференции end with -и? What case is that?

Конференции is the prepositional singular of конференция (a regular feminine noun in -я).

The declension is:

nominative (subject): конференция – conference
prepositional (location, after в, на): на конференции – at the conference

So на конференции literally means on/at the conference, and the ending -и is required by the prepositional case.

What is the function of есть here? Can I leave it out?