Hi Iris. A good place to start is with the center of the circle. Then it can be helpful to connect this to all the relevant points and label everything. An example of how this could go is below:

There's still some work to do here. As some additional hints, try to show the following:

1. $\triangle OBD\sim\triangle BHD$
2. $HGCO$ is a cyclic quadrilateral
   
3. $\triangle BGH\cong\triangle CGE$
   
4. $\triangle CEF\sim\triangle EBF$
   

Hope this helps a little more!