Hey Marius,
I make sportsbetting since 11 years and I can´t picture a live without it.
So in your place I would start with a sport where you think you have good informations or at least you knwo where to get them from (forums, newspapers, insider infos

, ....)
So lets say you chose soccer. Now you should focus on some leagues - lets say in your case romanian league.
It´s always better to pick one league where you can find good infos about that league, teams etc. in your language or the language you can understand.
After you pick some good matches and pick the type of bets you wanna make (win, over/under, handicap, etc...)
In my opinion you should start with the simple way - just pick the winner.
Now you should try to find the best odd - I can recommend you for example this site. BonusBonusBonus has in the livescore section a very nice odds comparison part. I heard they want to make it bigger but for the start it looks very ok for me. If you are not 100% happy with it, check out the gambling directory on BonusBonusBonus - there they recommend you some other good oddscomparison sites.
Just click next to your match the "odds icon" and you will get a list of bookmakers and the best odds for your game > this part is very important - don´t ever lose money on that part. You can just be a winner in sportsbetting when you consistantly bet good odds. When you lose your bet, it does not matter. When you win, it will be a big difference over all.
So that´s it for the start - I hope I could help you with my answer.
If you have any additional questions - just let me know.
Best Regards and good luck,
Maserati