The EMA (Exponential moving average)
(Revised July 01, 2011)
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In these tutorials I will discuss what to do when you visually look at a technical indicator or oscillator on a chart, I won't discuss math jargon or history, I think it's more important to know how to react at a glance (what is the chart saying), therefore only consider this an introduction in brief based on my opinion.  You should educate yourself further if interested. The charts used are not invitation to buy or sell, and are used only for example purpose.
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Intro
Basically the EMA is the average price people are willing to pay within a given time frame. The EMA is more reliable and reacts faster than the SMA (simple moving average).  The EMA is used to define the current market sentiment (i.e when people are willing to pay more or less for the ticker) and it can be used as "buy & sell" indicator.
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So how does it work?
The EMA line, when set to any time frame, flows along the chart as the PPS (price per share) moves above and below it.  Simply we can see each time the PPS crosses the EMA line we are given a "buy or sell" signal. The further the PPS moves away from the EMA line the more oversold or overbought the stock becomes; and therefore becomes more volatile.  At that point the PPS normally will find its way back to the EMA.
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Visually this is what the EMA is telling us on a 1 year chart with one EMA line set to 100days

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The Golden & Death Cross to find support & resistance
Using two EMA lines (example: one being set at 50days the other set to 100days). We see signals of when people are willing to pay more or less for the stock .  As the faster EMA (50) crosses the slower EMA (100)  we get a "buy or sell" signal and  a possible future "support & resistance" target.  Unfortunately this information is lacking the market by nature so you might want to set the EMA crossovers a little tighter as described below.

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Using a tighter time frame, 14/50day, it will give you a faster signal for active traders.  Below you can see the sell signal changed to end of April compared to near June in the previous chart. .  However, if you notice the arrow in the chart below, pointing to the fast EMA (14) that is starting to arc downwards; this could be an early warning sign telling you a decline may be coming and you can take the option to exit even earlier.
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How to use EMA Ribbons
By using more EMA lines set to different time periods, we can locate trends and "buy & sell" signals when one or more of these EMA lines cross over each other.  The difference is making the decision on how many crossovers must happen before the signal is official to the individual trader.  Overall a strong "buy or sell" signal is indicated after ALL the ribbons cross over.
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on the chart below I am using  20, 40, 60 and 80, but you can use more EMA lines or use different time frames

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So what do I think?
I think the EMA is one of the most reliable and easy to use technical indicators which can define the market sentiment.  And, I feel the Golden Cross and Death Cross can be safe "buy & sell" indicators especially when using ribbons, but for pinpointing a more specific entry or exit point the EMA may be lacking.
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The EMA time periods used are pretty much up to the trader's preference.
Some numbers to try are: 5/10day crossovers for day trading on intraday charts.  14/50day cross overs for short term trading and the 50/100day time periods for midterm.  The 100/200day EMA crossovers would be used more by long term holders, try it out and use what works for you.
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As with all charts and technical indicators you need  to pick a time frame and stick to it.  Don't pick one and trade in another.
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IMO, not one technical indicator can be used by itself.  The more indicators that line up to confirm the signal the better chances your trade will succeed.
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Good luck on all your trades and or investments
And happy capitalism