There's plenty of guys in the world that have massive cranks and have girls/wives leaving them everyday. A big sausage isnt the most important thing in the world, and most women find a lot more things about men attractive than penis size. Dont get me wrong, there are size queens out there and most girls dont complain about a dick being too big, but for the most part, the women that love us find so many things about us to be appealing or sexy, and penis is down the list a ways.
As far as where to begin, take a couple weeks to just read stuff on here, type in random things in the search box; 101, beginner, first, basics, how to, kegel, jelq, etc, etc.
Feel free to ask questions, but I was in the same boat as you. I stumbled upon this eutopia and had tons of questions, ideas and excitement zinging thru my head! Quite often I would post a new thread asking a question and I would find the answer somewhere else 10 mins later. I dont want you to confuse my words for impatient or rude. (sometimes its hard to read people thru text). The odds are that 99.9% of the questions you and I would have, are answered somewhere on this mass site. There's a lot of helpful guys on here. You see that real quick.
I personally recommend starting with kegels and jelqs for about a month. That's just me. It's a mild way to lightly condition you unit and it's uber helpful for erection quality as you start making gains.
God luck man