to get a new jabber account, it is necessary to download a jabber client and use it to register an account on a jabber server.
alternatively, you can use Jeti, a java applet which runs on this site, to register an account and also to use your account later on.
one of the advantages of jabber is that you can be connected to the same account with multiple clients at the same time. this means that you no longer need a 'work' account and a 'home' account, for example. different connections to the same account are distinguished by the 'resource' string, which you can set in your client software. instead of separate accounts you would then use a 'work' resource and a 'home' resource.
if you decide to not use an account anymore, please do not simply abandon it. try to use your client software to delete the account. most clients offer such a function.