Read theory before you ask.
You dont need any data you dont crack wep key so ivs are useless. You must capture packet which has 4-way handshake and then try get key form handshake with dictionary attack.
when client is is associating with ap then is your chance to get handshake so deauthentcion attack is there to make process faster by disconneting a clinet and force him to connect again.
In future read more before you ask because you ask basics which you can read anywhere.
Google: how to crack wpa key or better wpa wiki and wep wiki to see which key is made of what.