BeaLola:
Like all have said above there are many of us that are shy or like my name suggests 'older' Mums (although ancient may apply in my case).
I think the advice to smile at people - maybe say good morning will help. Remember that friendships take time and shared experience. As some have suggested - organise play dates or a birthday party. We found offering parents a coffee or tea at our DD1's YR birthday party and introducing ourselves and talking to them a bit about their child and their impressions of the school was a great way to 'break the ice'. I also found volunteering to help on field trips was also a good way of putting names to faces of my DDs friends.
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Now the other side of your post is that you don't really understand what should be happening. This is a failure of communication at your school (which many schools - ours included - are guilty of). They know what is going on and don't seem to realise they haven't made that very clear to the parents, especially new parents to the school.
Our school was very traditional and treated the first term of reception as a time to settle children into the school routine, start to assess their ability and begin to introduce more formal aspects of learning. More formal school work tended to pick up after Christmas.
To help you understand the main curriculum areas but with the health warning that this is ideal world stuff - I'd recommend you visit the curriculum pages for primary school on Campaign for Real Education: www.cre.org.uk/primary_contents.html. This should be seen as what could happen in a perfect world and your school will most likely not be working to this - but it does help to give you an idea of what is possible to cover at a given age.
Now Class R in my experience (DD1 now Y5/ DD2 now Y3) was about:
Settling into formal education
Learning social skills
Learning to follow rules
Starting to learn to read (we used Jolly Phonics)
Starting to learn to write
Starting to learn to count (to 20 or 30 but ultimately to 100)
More able pupils might learn number bonds to 10 or to 20 (by which I mean the following:
1 - 0+1 or 1 +0
2 - 0+2, 1+1 or 2+0
3 - 0+3, 1+2, 2+1, or 3 + 0
4 - 0+4, 1 + 3, 2 + 2, 3 + 1 or 4 + 0
and so on
Counting by 2s (also learning concept of even and odd numbers)
Counting by 5s
Counting by 10s can also be introduced at this age
All of these things can be supported at home - and there's lots of lovely resources on-line but try starting with Oxford Owl here: www.oxfordowl.co.uk/
At parent/ teacher meetings ask the teacher 'Is there anything we should be working on at home?' - and really make a point of listening (maybe noting it down) and then go away and gradually work away at whatever the teacher suggested (maybe sounding out words [possibly saying blending - so knowing c + l = cl and o makes almost an ah sound and ck makes a strong K sound which all together = clock), reading with more expression, predicting what will happen next in a story, making up alternative endings, etc... or working on maths areas (great with food, buttons, marbles, etc...) or playing maths based games like Snakes and Ladders or on-line games.
My four tips are:
Try and find out what the phonics scheme (the system of understanding how to sound out letters or groups of letters) is they are using and see if you can't help at home with some workbooks. Jolly phonics is very popular and there are some lovely workbooks with lots of colouring in to do which are available on-line through amazon or at most major bookstores/ newsagents.
Try and read together as much as possible. You may be doing most of the reading at first - but if your DS is starting to sound out simple one syllable words let him have a go now and then and gradually start to shift the bulk of the reading over to him over KS1 (Y1 and Y2).
Try and encourage as much counting as possible - and use games with dice where you have to add on 1 - 6 or 1 - 12 to move forward to start giving experirence of addition. When you get to subtraction play games like snakes and ladders backwards to practice counting back.
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If you're really confused about what you should be doing - talk to the teacher (catch them before school and say that you are very uncertain what you should be doing at home - could you maybe meet with them at some point to discuss what you should be doing?)
Now back to the first issue - not knowing anybody - you now have the ultimate subject of conversation for parents with older children in the school. Say hello and ask them if they've been at the school for a few years. Explain that you're new and really don't understand what is going on and then ask them if they can explain a bit more about what is happening in Year R. You'll find parents have all sorts of energy to discuss teachers/ curriculum/ etc... Take it all with a pinch of salt - but after talking to a few people you should have a better idea of what is going on and you'll have made some contacts at the school, some of which may bloom into friendships.
HTH