Spreads are a means of laying out the cards to do a reading. A number of cards are selected by various methods of shuffling, cutting or random selection of reader or questioner. The cards are then usually place in a specific pattern in which the reader intuits specific information pertaining to the person's need. Some believe that a true psychic doesn't need to do specific spreads and can read from any patterns of selected cards.
The following are a few examples of Tarot spreads and what they represent.
3 Card Spread

Position 1. - Past Event/Influence
Position 2. - Present Circumstance
Position 3. - Future/Outcome
5 Card Direction Spread
1.
2.
3.
4.
5.
Position 1. - Life direction as of current
Position 2. - Current lessons
Position 3. - What you are heading towards
Position 4. - Long term goals/objective
Position 5. - Assistance in getting there
4 Card Attainment Spread
1.
2.
3.
4.
Position 1. - What you desire
Position 2. - Skills/ Talents you possess
Position 3. - Blockages or what is lacking
Position 4. - Obtaining you desire
1 Card Spread
1.
Can be used for various questions.
Yes/No
Meditation
Card of the Day
Speak to Me
What time/month/year/season
Cards are read in both upright and reversal positions. It is usually up to the reader. Most authorities say that reading without reversals gives only some of the story. Reversals can definitely be seen as blockages, but some cards offer positive no matter which way the are turned. If read intuitively versus mechanically, the reader should be able to tell where the blockages or gray areas are with or without reversal.
I prefer to use my own interpretation of spreads but there are many excellent resources to investigate on the subject.
All Tarot Card images are from the Rider-Waite deck published by U.S.Games.