I suggest you learn some basics around the HTTP protocol.
Learn how authentication works etc.
Be aware that what we would call online cracking is not as awesome as it sounds.
Often its slow and depening on the password strenght it quickly becomes useless.
Alpha/nummeric 6 random digits would locally take a shit load of time let alone online, forget it.
Look into tools such as hydra/jack the ripper , get a linux box , do some toying around, bruteforce your router etc.