What should I present?

This should be a presentation of your own work. Ideally, it would be (a part of) your bachelor', master's, or doctoral thesis.
This of course does not presume that the thesis is finished.

I don't have any thesis...

Have you ever done any seminar paper on your own? Any class project? That could be suitable - check with me.

If not, choose a point of interest from a field you are fond of (e.g. financial mathematics).

• a problem that is discussed in your field, and methods of solving it
• explain a particular method used in your field, and its applications
• present a groundbreaking contribution of a mathematician
• find a thesis written by another student (in any language) and present what the person did
• etc. 

In case you are not presenting your own thesis, please consult your topic of choice with me before creating the presentation.

A word of advice: choose a mathematical topic that you understand. It is enough of a challenge to present it in English.

The idea of the context is that of a talk at an internal departmental seminar, informing other students and teachers from your department about your thesis. (Or an interesting problem that you are currently studying - in case you don't have a thesis yet.)

The length of the presentation is 20 minutes. (Do not upload presentations that are shorter than this.)