Can you connect to WiFi - “N” if your card only supports “B/G”?
Not pure 802.11n, there's a "mixed mode" that makes it compatible for these devices.
So if I have card thats only B/G and access point is B/G/N I still can connect in G mode?
It's rare for consumer B/G/N APs to only broadcast 802.11n, typically they broadcast all three unless you turn particular standards off. Otherwise they'd be called N APs, if B/G devices couldn't connect to them.
So yes, your B/G card will connect to the B/G/N AP. It should connect using 802.11g
So then if I have card that supports N card how I know I am in connected in right mode it choses highest it can automatically?