NOTE: d20 Fallout requires the d20 Modern Roleplaying Game, d20 Future and d20 Apocalypse books. Alternatively, you may use the  and the d20 Apocalypse book.
Step 1: Character Sheet
You may use a normal d20 Modern character sheet for your game. This means that you are most likely using either a paper character sheet, or an online character sheet such as those from MythWeavers. You may also use a piece of notebook paper, a text editor or a pdf.
Step 2: Ability Scores
Roll your ability scores according to the normal d20 Modern rules.
Step 3: Race
Next step is to select a race. Be sure to make the appropriate ability score changes and write down any special abilities you may have. Also write down your racial ECL (if applicable) in parentheses next to your level. Remember: Only humans gain two feats at level 1 and all other races gain one.
Step 4: Class
Now you must choose your class from the normal d20 Modern ones. Write down your hit points, action points and saving throw, defense, repution and base attack bonuses. Also mark down your class skills and choose a talent.
Step 5: Traits
A character may choose up to 2 traits. Traits may alter different aspects of a character's stats, typically in the form of a bonus and penalty.
Step 6: Occupation
Choose an occupation from the normal d20 Modern or Fallout ones.
Step 7: Skills
d20 Fallout uses the same skills as d20 Modern but have some new uses.
Step 8: Feats
A character begins play with 1 feat. The character may also gain feats from occupation, class and/or race. Feats give you bonuses or otherwise good effects. Players can choose from d20 Modern and Fallout feats. Note: In d20 Modern core rules, characters get 2 feats. This is due to all players being assumed human. In d20 Modern, humans still get 2 feats, but non-Humans only receive a single feat at first level.
Step 9: Equipment
Each new character begins the game with an amount of TUs/caps that can be spent on a wide range of equipment. Each character begins play with 4d10x2 TUs worth of items, or 10x that number in bottle caps to spend on equipment, and their occupation may add a TU/caps bonus. For default d20 Modern occupations, multiply the Wealth bonus by 2 for the number of bonus TUs (and again by 10 for caps).
Step 10: Finishing Touches
Finally, it is time to makes sure you added and/or subtracted all of your modifiers correctly. Also, humans may now roll for mutations/drawbacks (using the tables in d20 Apocalypse). You must also decide what your character looks like and what its personality is like. Some background is also useful. You may also pick an allegiance.