Use your imagination

First off, what do you like?  If you like one particular railroad, pick that.  If you have eclectic tastes (many of us do!) there's nothing wrong with running whatever you like.  Many of us also make up our own railroads (sometimes based on a real one, sometimes not) and go from there.

You have a few options

Really, it depends on what you want to do with your railroad.  Some things that come to mind-Whichever railraoad is closest to you, model a fictional line from that railroad that expanded into your area.  Or, you could pick a certain time and place to base your layout on.  How about buying non lettered engines and rolling stock, and painting them with your roads colors.  That can almost be a hobby in itself.  Or, you can start out the way alot of us do, buying whatever catches our eye, then weeding out the stuff we don't need later once we discover more specific times and places to model. 

non lettered engines and

non lettered engines and rolling stock? i'm so new that i didnt know the sell engines and rolling stock like that....

identity

Do you favor any certain area(or country) How about landscape? Mountains? rivers,lake,oceans? If you like a certain area do a search to see which railroads service it. What type of train do you like?freight?passenger,shortline,mining,lumber? What type of modeling do you like,scenery? structure building,track laying(hand),wiring?

All these things can point you to a specific railroad (dont forget era).And dont forget that the main goal is to please yourself.

john

here on my country we dont have trains

Perhaps you could invent some trains for your country? Make a railroad that fits into your local scenery and transportation needs? Narrow gauge line might be appropriate if the country is small and rural in nature.

 or perhaps a modern era "what if"" line with the latest freight diesels and passenger service?

 Building something you can identify with is usually more fun than building something you don't have any connection to..........DaveBranum

What everyone else said

What do you like?  ---> What is getting you into model railroading?  Just to enjoy trains go around (in a loop maybe) or do you like to make them go/stop here and there (dropping off freight at warehouses maybe)..it's all fair-game!  Realism, or realistic enough, or just plain fun- for YOU the CEO of this operation?

- Rule Number 1 - My Railroad, My Rules.

I encourage you to look around the internet, see what you like.  Ask yourself- Why do you like that?  Narrow it down and go from there.  Once that's decided, do some more research to see how that railroader did what they did,or how others have done similar things.  Then remember, you won't probably gets things right the first time.  Tight curves for the tracks (radius-s...radii?) are a killer for certain things for example.  It's all out there, especially at the NMRA website.  Lots of good stuff there, and not just 'Standards and Practices', but good stuff for the starter railroader as well.

History

Try writing a brief history of your fictional line. How it was started, where it runs to and from, etc.  Anything that you find interesting as far  as equipment, operations and such include it.  Use your imagination, include things you like, and finally use Joe's chainsaw method for building the layout. 

Start small and build the layout with the intention that you are going to salvage important parts; track, turnouts, structures electrical components, etc and scrap the rest.

Most importantly have fun with the LEARNING process and remember its YOUR layout.

...

Start with your country and design a railroad...