So, first off, I am completely new to the realm/s of D&D (playing and lore wise). I was encouraged by a friend to play so that their party was better filled, and I had heard of D&D with nothing more than rumors, so I decided to give it a go and build a character. My first step into this sea... was more like stepping into a deep trench. I find myself looking for specific details only to discover that some details depend on certain realms; like the difference between The Forgotten Realms and Eberron. Wading in for knowledge I seek has left me drowning and lost.

What I want for my character's backstory is for him to be of a human unnamed minor noble house, one that is not too significant but known well enough to be in the social circles of the aristocracy. Any advice from experienced players would help my predicament.

I just hope I did this thread right.

Which setting: Eberron or Forgotten Realms? Where in that world? 

The best solution is to ask your DM. They will know how to best integrate your backstory into their game, setting, and campaign.  Maybe they have a story/idea in mind that they can integrate with your backstory.

We all start somewhere, and honestly a lot of us are still lost and trying to learn as much as we can. Your best option here is to write up a vague backstory and then talk to your DM. They will know the world better than any of us, because we need to know what setting you're using to fully help you. 

But, think about what traits your character would ideally have and then write how they happened. If your character was an only child to a doting family, would they like to be centre of attention or avoid all of the attention possible? How about if their family didn't even notice them because they were the last child? Are they setting out on an adventure to make their parents proud or to prove their worth? Will anyone recognise their name, and if so, will they go by a different one? Would they treat lower classes (servants, etc) with kindness or will they forget that they're also people? 

Once you've decided on their class, think about why they chose that one in particular. Did they get weapon training as a kid, and will that make them cocky using a weapon in the real world? Or are they more into reading books, and do they spend their money on them? How about magic, did their parents pay for tuition? Or did they discover their magic by accident? Would their parents have hidden their talents, or not have noticed them, or be incredibly proud? 

Having a chat with your DM once you have a vague idea of what you want will clear a lot of things up. Your DM will help guide you into a backstory that makes sense in the world, and you'll give them ways to get your character to interact with the world on a more meaningful level. 

The nice thing about D&D is that individual games are usually unique.  Don't worry about whether the other players have ever heard of your noble house, just make sure you tell the DM.

Easiest way to start, look at a map of the world you are playing in, pick a city that seems interesting to you.  It could be interesting because of its name, location, whatever.  Then either come up with your backstory about them in that city, or google the city or use one of the D&D wikis out there to get the information you are looking for.  Then you can come up with a reason as to why your character is where the current game is taking place.

As the others have also said, communicate with your DM.

I've had this concept adapted for Dune called "lost houses". The idea was during the War of Assassins many minor houses were simply wiped out. But not all of them went extinct.

In that universe, the lost houses made it to Dune, where they became smugglers and made a rather vulgar provincial living where once they were nobility. 

So perhaps your Character is also on the run. And being known by the rest of the world isnt necessarily ideal to you. So while maybe you have some perks of your minor house, they are not immediately available to you