Can't decipher capture file

I'm playing with airodump-ng and wireshark (I'm not a networking specialist). I have captured some packets from my network with airodump-ng and wanted to open them in wireshark, but they seem to be gibberish (instead of HTTP requests and stuff).

This was my order of operations:

1. Run airodump-ng --bbsid <myRouterMac> -c 1 -w <filename> <interface> --output-format pcap, make some requests in browser (http, not https) and Ctrl-C.
2. Open Wireshark and open the file.
3. Add WPA-PSK generated key from Wireshark website generator.
4. Experiment with options

I expected this to work, but it's not working. What may be the cause? What I have to do to make it work?