We have 3 parents evenings a year. The first is (for most classes) just a "how are they settling in, any concerns?" discussion especially for Reception parents. The second (February) evening is much more about strengths and weaknesses, areas to concentrate on, things to look out for. The third (in July) is a post report drop in session to discuss any concerns, worries for next year etc.
What I found reassuring with the first parents' evening in Reception is that the child the teacher was describing was definitely MY child - it gave me great faith in the ability of this woman to know the 31 little children she had charge of, and assured me that DD was being 'herself' in school.
Not much to learn really other than how your child has settled in and probably be shown some of the work they've done. It's all very sweet and reassuring (hopefully!) and I always used to rather enjoy the first parents' evenings! (sentimental sigh)
(My 3rd dd through reception in 4 years with the same excellent teacher)
"she's very different to her sisters" "she's very confident with her speech even though it can be difficult to understand" "yes she needs to be on the SEN list" "She's a model pupil" (naughtiest of my 4 dc at home!)
As above I expect them the describe my little girl and if they don't I'll be concerned.