No idea how to succeed cracking hashes

[Jiminy]

First off, no one knows if the password they are looking for is in the wordlist they're using.  That's why you have numerous wordlists and keep trying.  That failing, use wordlists with rules.  There are numerous examples of using rules in the wiki and FAQ.

Perhaps you should try to crack some of the example hashes listed on the "example hashes" link about half way down the wiki page.  All passwords are [ hashcat ] (without the brackets) with exceptions noted.  
Also on the wiki page there are numerous references to using each of the attack modes. Follow the examples and adapt to each new situation.  The FAQ has a plethora of information on using hashcat.  It's a good read with examples and answers many questions.

READ, READ, READ. then READ some more and PRACTICE, PRACTICE, PRACTICE.
Good luck.

Greetings!
I'm new here, but I've used hashcat before.

My problem, which is giving me a huge headache, is that I can't succesfully crack anything!
I'm here to ask for help and advices.

So far, my use of hashcat has been with wordlists, straight attacks, but as you can imagine, I found nothing.
I would love to crack some hashes, but I don't know how to move. Can you please help me, telling how do you do it?

For example, how can you crack an MD5? I am 100% sure you use a rule or something like that, but I have no idea. Also, my wordlists are big (>5Gb), so I think they are pretty useless if I'm not sure the password is inside that file.

Another example, how to crack a wpa2? Usually, I search for the router name, find some passwords and make a mask on that. But what if that has been changed? how can I crack it?

Hope you can help me, because I'm lost.