METAR, loosely an acronym for Meteorological Area Report are weather reports (not forecasts).

How to decode a METAR:

For this explanation, I'll be referring to the current metar for my hometown's airport:
CYXX 070700Z 00000KT 15SM BKN050 OVC100 10/07 A3007 RMK SC6AC2 SLP184

A METAR consists of several parts. The first of which is always the station identifier
CYXX ICAO code for Abbotsford, BC, Canada

The second is the current date and time, calculated in GMT (zulu time)
070700Z Starting with the date, which in this instance is the 7th, and then going on to the time, which is 0700 GMT

And then, on to the actual weather report, starting with wind direction (in degrees), then wind speed (given with the final 2 or 3 letters), possibly with gusts after it, marked with a G
00000KT Winds are at 000 degrees, 00 Knots (KT) (if there were gusts, it would read something along the lines of 24602G05KT, winds at 246° at 2 knots, gusting to 5 knots)

Next, is visibility
15SM 15 Statute Miles, other available scales could be NM (nautical miles) or KM (kilometers)

And after that is weather elements
no example available on this metar
These are the, ahem, fun bits.
Weather conditions always start with an intensity/proximity modifier. + for heavy, nothing for moderate, - for light, and VC for in the vicinity.
After that, possibly, is a descriptor, which is a 2 letter code for any special parts of this particular weather element.
Weather elements can be divided into 3 different groups. the first is Precipitation: The second is obscuration And the last is "other"
After the weather elements, is the sky condition. Sky condition is given a condition code, then a layer level (in hundreds of feet) culmunative (as in, you can't have a "few" layer after a "broken" layer. if that few layer closes off the broken parts of the sky, it becomes an overcast layer)

If none of the sky is covered at all, the code is simply SKC (for sky clear).
If 1/8 to 2/8 of the sky is covered at the given layer the condtion code is FEW
If 3/8 to 4/8 of the sky is covered, the condition code is SCT (for scattered)
If 5/8 to 7/8 of the sky is covered, the condtion code is BKN (for broken)
If 8/8 of the sky is covered, the condtion code is OVC (for overcast) and no further layers are given
BKN050 OVC100 Broken at 5,000 feet, Overcast at 10,000 feet

After the sky condtion comes temperature and dewpoint, given in degrees Celsius, in the format Temperature/Dewpoint. sub-zero temperatures will be preceded with an 'M'
10/07 A temperature of 10°C with a dewpoint of 7°C

Next is Sea-Level barometric pressure, preceded with an 'A', and calculated with inches of mercury
A3007 30.07"Hg

Finally, is the remarks section, given in plain language or special acronyms, which starts with the RMK acronym.