Now you have to wait for a while, till you have captured enough data to crack the WEP key. If the access point is busy then you might not have to wait too long. Anyway, after an hour or so, you can try cracking it. Type: aircrack-ng mycapture-01.ivs and hope for the best. aircrack will try to crack the key, and if you have enough data captured it should crack the key eventually. If not, it will keep trying, as you gather more and more data, until you are successful (or never if you are unlucky, or if there is not enough traffic on the network)