It's really simple but confusing.
I want to start in bitcoin mining NOT as a hobby, but as a serious issue where I can have profit from.
Yes. You are confused. In order to make a profit mining bitcoins, you have to understand how mining works. If you don't understand, you will lose money. So, if you want to make a profit, you must first learn how mining works, including the economics of mining.
For example, you probably don't realize that a 7970 mines less than $20 a month right now, and in 6 months it will be mining less than $1 per month. Even if the electricity is free, a 7970 will never pay for itself.
http://mining.thegenesisblock.com/This site is an excellent tool for choosing mining equipment. It will help you determine how much profit the different kinds of mining equipment will make.