Stats in DDO have a base of 8, which grant a -1 modifier.

Bonus/Penalties come in steps of 2. Having only 8 points in a stat will result in a -1 modifier and 12 will result in a +1 modifier.

Most stats start at 8 during character creation and can be increased with build points. A new account allows only a 28 point build. Increasing each stat costs more and more points the higher you raise it.

Each stat may be raised a total of 10 points.

Adding 1 to a stat costs 1 point
Adding 2 to a stat costs 2 points
Adding 3 to a stat costs 3 points
Adding 4 to a stat costs 4 points
Adding 5 to a stat costs 5 points
Adding 6 to a stat costs 6 points
Adding 7 to a stat costs 8 points
Adding 8 to a stat costs 10 points
Adding 9 to a stat costs 13 points
Adding 10 to a stat costs 16 points

A 32 point point build can be unlocked once a character has reached 1750 total favor.

A true reincarnation of a 28 or 32 point build character will allow him to be re-built as a 34 point build.

A true reincarnation of 34 build character will allow him to be re-built as a 36 point build.

Each race has different base stat mods:

Aasimar (+2 WIS)
Assimar Scourge (+2 WIS)
Bladeforged (-2 DEX / +2 CON / -2 WIS)
Deep Gnome (-2 STR / +2 INT / +2 WIS / -2 CHA)
Dragonborn (+2 STR / -2 DEX / +2 CHA)
Drow Elf (Automatically a 32 point build): +2 DEX / -2 CON / +2 INT / +2 CHA)
Dwarf (+2 CON / -2 CHA)
Elf (+2 DEX / -2 CON)
Gnome (-2 STR / +2 INT)
Halfling (-2 STR / +2 DEX)
Half-Elf (No mods)
Half-Orc (+2 STR / -2 INT / -2 CHA)
Human (No mods)
Morningload (-2 CON / +2 INT)
Purple Dragon Knight (No mods)
Razorclaw (+2 STR / -2 WIS)
Shadar-kai (+2 DEX / -2 CHA)
Shifter (+2 DEX / -2 WIS)
Tiefling (+2 CHA)
Tiefling Scoundrel (+2 CHA)
Warforged (+2 CON / -2 WIS / -2 CHA)
Wood Elf (+2 DEX / -2 INT)

Strength is the primary stat for almost any melee character.

Your strength bonus adds to your to-hit and damage with most melee weapons.
Each strength modifier point (every even stat point adds another modifier) increases your to-hit and damage by one point.

The jump and swim skills are based on the strength modifier.

Rangers get a feat called Bow Strength at level one. Other characters may select this feat later. The bow strength feat allows your strength modifier to be added to your bow damage, just like most melee weapons.

Characters wielding two-weapons receive half of their strength modifier on their off-hand weapon attacks.

Characters wielding a two-handed weapon receive one and a half their strength modifier to weapon damage.

Thrown weapons add your strength modifier to damage, but use your dexterity modifier for the to-hit bonus.

Required for the following feats:
Power Attack (13+)
Two Handed Fighting (15+)
Improved Two Handed Fighting (17+, BAB 6+)
Greater Two Handed Fighting (17+, BAB 11+)
Oversized Two Weapon Fighting (12+)

Your dexterity modifer is added to most range to-hit.

Your dexterity modifer is added to your armor class, capped by your armor's max dex modifier.

Your dexterity modifier is added to your reflex saving throws.

The following skills are based on your dexterity modifier:

Balance, Hide, move silently, Open Lock and Tumble.

Required for the following feats:
Manyshot (17+)
Improved Precise Shot (19+)
Precision (13+)
Dodge (13+)
Mobility (13+)
Weapon Finesse (13+)
Two Weapon Fighting (15+)
Improved Two Weapon Fighting (17+, BAB 6+)
Greater Two Weapon Fighting (17+, BAB 11+)
Rapid Shot (13+)
Shot on the Run (13+)
Shuriken Expertise (13+)
Combat Archery (17+, Point Blank Shot, Level 21+)

This is probably your most important stat.

Your constitution modifier determines your hit points on all characters.
Your constition modifier is added to your fortitude saving throws.
The concentration skill is based on your constitution modifier.

For most characters it is recommended that you start with at least 14 CON.
Advanced players will often use a lower CON, but when starting out, at least 14 is a good rule of thumb.

Required for the following feats:
Resilience (13+, BAB 1+)
Epic Toughness (21+, Toughness, Level 21+)

Your intelligence modifier gives you +1 skill point to spend when you level up.

The following skills are based on your intellect:
Disable Device, Repair and Search.

This is the primary stat for Wizards and Artificers.
As the primary stat, the intellect modifier increases your spell points and the DC of your spells.

Required for the following feats:
Combat Expertise (13+)
Insightful Reflexes (13+)

Your wisdome modifier adds to the following:

Will saves

Monks gain their wisdom modifier add to their armor class and their stunning fist DC.
Some runes require a certain amountof Wisdom to activate.

The following skills are based on Wisdom:
Heal, Listen and Spot.

Spell points for Clerics, Paladins, Druids and Rangers are all based on this stat.

Rangers, Clerics and Palidins require a minimum of 10 + level of spells (At least 14 Wisdom will be required to cast level 4 ranger spells)

Favored Soul and Clerics add their Wisdom modifier to their DC checks of many of their spells.

Required for the following feats:
Zen Archery (13+, BAB 1+)

Charisma is the base of many useful skills:

Bluff, Diplomacy, Haggle, Intimidate, Perform and Use Magic Device.

Clerics and Paladins add their Charisma modifier to their Turn undead checks.

Paladin's Lay on Hands ability heals them for their Charisma modifier * character level.
The Paladin feat granted at level (Divine Grace) two allows your character to add your charisma modifier to all of your saves.

Sorcerers, Bards and Favored Souls all gain bonus spells points based on their Charisma modifier.

Sorcerer's and Bards add their Charisma bonus to many of their spell DC's.

Required for the following feats:
Force of Personality (13+)