1998 Opel Astra errror code ' S ' blinling in the dash boar

Sir,
i hav an opel astra 1.6 petrol auto transmission 1998 model sometimes it blinks error code as 'S' in the dash board and the car pick automatically comes down we need to use more power to run the car and when we come to stand still it will not move we have to move in manual gear mode?

In the gear shift rod i hav option starting from parking reverse neautral drive then three two and one some people say we can use manual whn automatic doesnt work like 1 2 3 gear my doubt is that can i shift from maual 3rd to drive whlle running or i hav to stop and use the drive mode?