Steps to becoming an IFBB Professional Bodybuilder
1. Choose the IFBB affiliated federation for your country. You cannot compete in a federation of another country - you have to compete for your home country, or where you have citizenships.
2. Compete! Start competiting as soon as possible - there is nothing as inspirational as competiting against other bodybuilders win, lose or draw! You will progress as a bodybuilder far quicker if you compete than if you don't. If you keep putting off competiting 'until you are ready' then it is likely you will never compete at all. Start in the First Timer (or equivalent category) and work your way up.
3. Win a regional contest weight class. When you win or place highly (and thus get invited) you earn an invite to compete at your federations National Championships contest for that year. This means that you get to compete in the weight class you qualified in, and if you win at the Nationals then you are the best bodybuilder (the Champion!) in your class in your federation for that year! Quite an achievement. The winners of each weight class will the go head to head in a separate contest to see who is the overall Champion for this year.
4. Earn an IFBB Pro Card. Depending on your federation, the overall Champion will be offered a pro card. Some federations offer Pro Cards to winners of individual weight class champions too (though normally the heavier classes only). This can mean that each year more than one bodybuilder may earn a Pro Card.
There are other ways besides your National Championships contest to win Pro Cards - you can win at the IFBB World Bodybuilding Championships. This is a drug tested event, so only the best natural competitors from each countries IFBB affiliated federation are entered. Ronnie Coleman, 8 times Mr. Olympia won his IFBB Pro Card at the World Bodybuilding Championships, and Dorian Yates once competed in this event too. This is probably the only viable way to win an IFBB Pro Card while natural.
Another way is that sometimes a particular IFBB contest may hold a special amateur contest where the victor wins a Pro Card and gets to compete that same night in the Professional contest.