The doji is quite similar in it's make up to the spinning top. The common theme they share is that they're both examples of indecision in the market.
If you google "doji candlestick pattern" or something along the lines of "common candlestick patterns" you should bring up a bag full of info surrounding the patterns.
I've included a recent chart of the EURUSD highlighting the doji (rectangle) & spinning top (circled) examples as a primer for you.
You'll find that these types of candle prints tend to offer clearer & more reliable trading signals when they reflect the psychology of market participants on or around area's & zones of fair value or previous levels of support & resistance.
Basically, buyers & sellers are in agreement that the level represents a stand-off & the resulting behavior can often mark the resumption of the next stage of the price journey (either continuation or reversal).
Their reliability (apparently) also increases the higher up the chart timeframe grid they show their hand. In other words, a doji or series of doji's and/or spinning tops printing on a Daily chart reference on or around a big figure (00) tends to trump the same combination forming on a 5 min chart timeframe.
It's not particularly
what type of candle formation is printing, but
where & why it's printing that matters most