I apologize in advance if I am making an incorrect assumption, but judging by your writing, you are not a native English speaker, so aren't an American (or UK, Canadian, Aussie, etc.) citizen. Every country with a manned space program recruits only their own citizens (so far) as astronauts. NASA astronauts are all American citizens (some are dual-), so any advice for NASA would be for Americans only.
If your country of citizenship is Canada or part of the EU , you can take a look at the CSA or ESA (respectively) requirements (which are pretty much the same as NASA's). Russia, and possibly some of the former SSRs, tend to recruit from the military, so you would have to have a successful career in the Cosmonaut Corps to be selected to fly a space mission. I believe that China has a similar military tradition (although that may change with Tiangong). The Indian manned program is selecting from their Air Force.
Finally, if you are not a citizen of the US, Canada, EU, Russia, China, or India, you would need to pay your own way to space, which can be as cheap as $450,000.