What the Numbers Mean (PHB)

Now that you have finished creating the ability scores for your character, stop and take a look at them. What does all this mean?
Suppose you decide to name your character "Rath" and you rolled the following ability scores for him:
Strength 	8
Dexterity 	14
Constitution	13
Intelligence	13
Wisdom 	7
Charisma 	6
Rath has strengths and weaknesses, but it is up to you to interpret what the numbers mean. Here are just two different ways these numbers could be interpreted.
1) Although Rath is in good health (Con 13), he's not very strong (Str 8) because he's just plain lazy—he never wanted to exercise as a youth and now it's too late. His low Wisdom and Charisma scores (7, 6) show that he lacks the common sense to apply himself properly and projects a slothful, "I'm not going to bother" attitude (which tends to irritate others). Fortunately, Rath's natural wit (Int 13) and Dexterity (14) keep him from being a total loss.
Thus, you might play Rath as an irritating, smart-alecky twerp forever ducking just out of range of those who want to squash him.
2) Rath has several good points—he has studied hard (Int 13) and practiced his manual skills (Dex 14). Unfortunately, his Strength is low (8) from a lack of exercise (all those hours spent reading books). Despite that, Rath's health is still good (Con 13). His low Wisdom and Charisma (7, 6) are a result of his lack of contact and involvement with people outside the realm of academics.
Looking at the scores this way, you could play Rath as a kindly, naive, and shy professorial type who's a good tinkerer, always fiddling with new ideas and inventions.
Obviously, Rath's ability scores (often called "stats") are not the greatest in the world. Yet it is possible to turn these "disappointing" stats into a character who is both interesting and fun to play. Too often players become obsessed with "good" stats. These players immediately give up on a character if he doesn't have a majority of above-average scores. There are even those who feel a character is hopeless if he does not have at least one ability of 17 or higher! Needless to say, these players would never consider playing a character with an ability score of 6 or 7.
In truth, Rath's suitability has a lot less to do with his ability scores than with your desire to role-play him. If you give up on him, of course he won't survive! But if you take an interest in the character and role-play him well, then even a character with the lowest possible scores can present a fun, challenging, and all-around exciting time. Does he have a Charisma of 5? Why? Maybe he's got an ugly scar. His table manners could be atrocious. He might mean well but always manage to say the wrong thing at the wrong time. He could be bluntly honest to the point of rudeness, something not likely to endear him to most people. His Dexterity is a 3? Why? Is he naturally clumsy or blind as a bat?
Don't give up on a character just because he has a low score. Instead, view it as an opportunity to role-play, to create a unique and entertaining personality in the game. Not only will you have fun creating that personality, but other players and the DM will have fun reacting to him.