The Doji  is a single day pattern. It is a single candlestick where the open and close price is equal or very close to be the same. 
Doji indicates indecision in the market and is considered as a trend reversal pattern. 
Psychology of Doji pattern is 
When  a market is at an uptrend and a Doji appears then neither the bears nor the bulls have the ability to push prices in their direction.  This inability or indecision to move the markets in one direction will be seen as a trend change candlestick pattern.

For example, if Doji appears after an uptrend, it shows that bulls are unable to push prices much  higher  resulting in traders deciding to sell and pushing the asset  prices lower. This is a Doji  Top Reversal  Candlestick. 
If Doji appears after a downtrend, it shows that bears are unable to push prices much lower resulting in traders deciding to buy and pushing the prices of the asset higher. This is a Doji  Bottom  Reversal  Candlestick. 

The long legged doji is a doji with long upper and lower shadows. When a long legged doji has the open and close in the middle of the upper and lower shadow, it is referred to as a rickshaw man. Dragonfly Doji and Gravestone Doji are other types of Doji.

Doji Doji-1 Doji-2 Doji-3

Practice Doji – Beginner

Practice Doji – Intermediate

Practice Doji – Expert