I know exactly how you feel. My dd is 7 now, but I can remember so clearly how I felt when she started school.
I went from knowing everything - nursery would let me know what she had eaten, what they had done that day etc. etc., to knowing nothing. There was no induction for parents to say what the structure of the day was, no weekly plan of what they would be covering that week - or at least an idea would have been helpful, we could always then do something connected or discuss it at home.
The only time we had feedback was at parents eve. twice a year. We weren't even allowed in the classroom, not on the first day of school, or after, we waited outside the door on both drop off and pick up. To make it worse, the blinds in reception were never opened, so you couldn't even see them in class when we went to pick up.
Honestly, I felt she had been 'ripped' from me and thrust into this weird world, that I had no knowledge of and I expect this is excatly how you are feeling. You don't know if they eat at lunchtime, whether anyone helps, what is the structure of lunchtimes - trying to get information from a 4 year old is impossible!
I asked the teacher for more information, but they just said it wasn't school policy to issue work plans to parents, I didn't want that, just an idea of what she was doing!, but I didn't want to make a fuss and be 'that' parent!
One way, I did find out a bit more, was doing some role play at home, playing schools using her toys as the children and she was the teacher, I found out they had 'group worship' in the morning and that they had a Black Cloud if they were naughty!! I also found out they had time in various areas during the day - construction area, art area, home corner etc., and that the teacher would read a book at the end of the day.
I suppose if you have already gone through the system with one child, you may know this, but I hadn't and didn't, when I got her reading book and the notebook with it, I had no idea that I had to write and comment in it - no one told me!!!
It does get better, as they get older and you start to talk to mums and hear a bit more. However, do go and talk to the teacher and tell her your concerns, I so wish I had made more of it now....
Not all schools are like this, some give great feedback and little newsletters each week saying what they have done and opportunities to go in - Ours didn't and it was 'outstanding'!
Hope it gets easier, try talking to other mums, that really helps too.