1. Write some software
2. Sell some copies
3. Repeat until wealthy
All the rest is just details...business licenses, tax id's, banking, that vary widely from place to place and country to country and usually require lawyers somewhere. Then business locations, staffing, equipment, etc. that are pretty standard. My advice: hook up early with a good accountant and a good lawyer. Second advice: make sure you have a product to sell before doing any of the rest of these details.
Of course, there is also:
1. Find some guy who wrote some software
2. Sign a distribution deal
3. Sell some copies
4. Repeat until wealthy
For the cynical (tongue planted firmly in cheek):
1. Talk about some software you're going to write until someone gives you money to develop it
2. Start to develop the software
3. Talk about costs and overruns until you get more money
4. Repeat (3) until a. You finish or b. You run out of money
5. Repeat until wealthy or bankrupt
Good luck on your new business! I really hope you do well.