Skills in Fallout 3 are used to indicate your ability to complete tasks. They are initially based on your SPECIAL attributes, and can train them on each of your 19 level increases. You can also read skill books to improve these skills as well; these books are scattered throughout the wasteland.
In addition to providing a base benefit, you can sometimes get special dialogue options if you have a high skill. It may also be required to complete some objectives as well.
Barter
Charisma skill. Affects your ability to get good deals from merchants.
Big Guns
Endurance skill.
Energy Weapons
Perception.
Explosives
Perception.
Lockpick
Perception.
To pick a lock, you first need to meet the requirement to pick the lock (e.g. skill 25 for Easy, 50 for Average, 75 for Hard and 100 for Very Hard.) If you meet this requirement, you are shown a close up of the lock. To pick a lock, you need to align the bobby pin in the correct location within a 180-degree arc. Press left or right to turn the lock.
If the bobby pin is off position, the lock will stop. Release the force and adjust the bobby pin to try again; if you are getting close, the lock will turn a bit further.
Each bobby pin can only receive a limited amount of force before it snaps.
You also have the option to force the lock. This has a random chance of succeeding, as shown on the screen. If you fail, the lock is broken and you can't attempt to open it again without the key.
Medicine
Intelligence skill.
Affects bonuses from stimpacks, Rad-X, and Radaway.
Melee Weapons
Strength skill.
Repair
Intelligence skill.
Repair affects your ability to repair items that you carry by taking parts from other items.
Science
Intelligence skill.
The science skill gives you the ability to hack into computers. If you meet the requirement (e.g. skill 25 for Easy, 50 for Average, 75 for Hard and 100 for Very Hard) you are presented with a memory dump that lists potential passwords.
To start, select a password in the list. You are presented with a number of characters in their correct position; your future guesses must have exactly the same number of characters in your previous guess.
If you make four wrong guesses, the system locks and you cannot access the system without the correct password. However, you can avoid this simply by stopping the hacking attempt before you choose the fourth password, or by obtaining the appropriate perk.
Small Guns
Agility skill.
Speech
Charisma skill.
Speech allows you to go through special dialogue options. If you have an option to do a speech attempt, you are shown a percentage chance of it succeeding. This percentage is checked against the difficulty of the speech attempt, and passes if it's equal to or higher — there is no random chance involved.
The best method to increase chances of success is to wear apparel that boosts speech or charisma.
Sneak
Agility skill.
Sneak allows you to remain undetected when in stealth mode. It also allows you to pickpocket or plant grenades or mines on people.
Unarmed
Endurance skill.