Character guidelines

Characters are power level 6, and generally follow the guidelines for such characters as given in the Mutants & Masterminds 2nd Edition rule book. Power level 6 gives you 90 Power Points. This places limits on a number of things, but note that it does not directly limit the cost or number of ranks in a power.

Mutants & Masterminds Character Builder
You will find character creation much easier if you use the Mutants & Masterminds Character Builder. It requires OpenOffice (which you should be using anyway).

Backgrounds
Each character has one racial background. In addition, humans also have one cultural background.

Equipment
Spells and any other inherent abilities must be purchased with character points. Mundane equipment must be purchased with silver. Extraordinary equipment must be obtained through in-game actions. Note that it is possible to exceed the power level caps through the use of equipment, but not through spells.

Magic
If your character can use magic in any way, read the Magic section.

Abilities
Take a look at the power level caps. Note that in a PL6 game, a number of traits are limited to a maximum of 6, even after adding a feat such as Lionheart or Attack Focus. Also keep in mind that you can trade off your maximum Attack bonus with your damage DC (which, unless you are a magician, means your Strength modifier), and that you can trade off your maximum Defense bonus with your max natural Toughness save (which, unless you are a magician, means your Constitution modifier).

Now, all of that being said, you don't need to max out their stats to have viable characters. If your character is not a toe-to-toe combat monster, it is perfectly reasonable to have Attack and Defense of 3 or 4. You might then have a few feats which can increase this to 6 when the circumstances favor the character (e.g., Attack Focus, Attack Specialization, Dodge Focus, etc.). Similarly, if you do not envision your character as a musclebound hulk, it is perfectly reasonable for your character's Strength modifier or Constitution modifier to be 3 or 4 (or even lower). Again, you might then have a few feats which which can increase the character's Strength-based damage DC or natural Toughness to 6 when the circumstances favor the character (e.g., Defensive Roll, Sneak Attack, Dirty Fighting, etc.).

Saves
Take a look at the power level caps. Note that in a PL6 game, Fortitude, Reflex, and Will saves are limited to a maximum of 11 (after including the attribute bonuses for Constitution, Dexterity, and Wisdom). However, you do not need to max out all of these. A perfectly viable character might have +5 (plus the attribute modifier) in one saving throw, and +2 (plus the attribute modifier) in the other two saves.

For example, a wizard might have +5 on Will saves, and +2 on Reflex and Fortitude saves (plus attribute modifiers). A swordsman might have +5 on Fortitude saves, and +2 on Reflex and Will saves (plus attribute modifiers). And so on.