There isn't really a direct question here, so im not sure what your asking for. Remember.... always Google your question before posting.... just so you have an idea of what your talking about instead of being spoon fed.
First, MAC filtering is not specific to wireless networks, any kind of LAN environment with the right software can filter peoples MAC addresses from the network.
Second, Technically, yes MAC filtering only allows the computers with specified MAC address's to connect to that Access point, however there are ways of getting around this without changing your MAC.
Third, May i suggest Kismet instead of airodump for gathering MAC's... do a little research and you'll find out why.
Fourth, Yes you can copy a computers MAC that is connected to that network, spoof your own and than connect, however it wont work if there are two computers with the same MAC on the network. You will need to deauth the client than take their spot. Again, this would be a very noticeable attack, because when the legit user try's to reconnect, this can cause them to go offline, or you depending on network traffic.
Again, not sure what you were asking so hope this helps.