Need help regarding ssb tech interview

I have been called up for navy tech-engineering ssb interview (Btech 4th year). I'm very new in this and have no idea about how these interview works. Will there be an physically challenging tasks for engineering branch?. In my call up letter ,instruction is provided as below

Stage I. The Stage I testing shall commence at 06:30AM on the first day and will comprise of an Intelligence Test and a Picture Perception and Discussion Test (PPDT). In case of rejection in Stage I, the candidates shall be returned from the Selection Centre in the afternoon of the same day. Stage II. The Stage II tests comprises of Psychological Tests, Group Test I & II and Interview for maximum of 04 days.

What does Group test 1&2 means ?? im not very physically active ,and have low acads, so what will be needed to focus from now on?