How can I fix my Parkside PKS 40/5?

Hi
Ive just been given an electric Parkside PKS 40/5 chainsaw.
Ive cleaned it up and it all moves fine by hand however there is a reservoir which I am presuming is for oil(?). If so what sort do i need to put in it, I realise it may be a dumb question but Id rather be safe than sorry. Thanks

Bob Gregory
February 2016