A tarp, is, in essence a simple sheet of something weather proof, beyond that you get varying degrees of luxury.
- Attachment points - these vary from metal eyelets on ponchos, upto strong reinforced webbing loops. They also vary from one in each corner to a dozen or so spread around the edge and even in the middle
- Material - Again these range from cheap low end plastics that will degrade in UV light, tend to exist in BRIGHT COLOURS that have all the subtlety of a torch to the eyes, right up to ultralightweight cuban fibre. At which point in this range you want to put your coin, will be your choice.
- Reinforcements - Some tarps come with funky reinforcement webbing and the like. Useful if you are likely to be out in bad weather.
- Shape - Not all tarps are rectangular, some are kite shaped, some trapezoid, all sorts of other wacky shapes. I prefer the rectangular ones, IMHO, more versatile.
- Secondary uses - Some ponchos work well as a tarp, I used a Germany army Flektarn poncho as my tarp for a number of years. Others, like the British Army Basha can double as a stretcher (not a feature I've had to use... yet...)
- Size - The smallest commercial tarp I have found is 1.4m x 1.2m. Most tend to be around the 2m x 3m mark, the reason I upgraded from the poncho mentioned above to the Basha, was it was a bit bigger so I didn't have issues if the rain was anything other than vertical. Hammock camping most people seem to go for a 3m x 3m tarp as this gives them the length to stay dry, with the cover to the sides to keep the rain/wind out. Smaller tarps tend to be used with a bivvi bag to give some protection over the head area, with the primary aim being to give some protection to your head. The largest backpacking tarp I can find is 4.5m x 4.5m...
So, with all of that, what are the options.
- Military issue Poncho - Pick your army and they probably make a poncho, I have the German one, but the Brits, Americians etc... make good ones.
- Military issue Basha/Tarp/Hoochie - Again, pick your army, they probably make one. I have the British Army Basha as my main tarp these days, it doubles as a stretcher, has lots of reinforcement as well as a multitude of tie down points
- Noname camping tarps - These are the sort you find in tesco, wilko and decathlon, at varying prices, the cheap ones will work for the first night. I wouldn't want to place bets on the the second night for one from tesco or a pound shop...
- Ground sheet - Many of the ground sheets sold in camping shops will work as a tarp, but they will weigh a ton, but they do tend to be cheap.
- Specialist backpacking tarps - These you can find from the likes of
Backpackinglight,
DD,
Alpkit, this is where you are going to find the unusually shapped tarps, as well as the exotic materials, it's going to be more expensive, but the weight is going to be very low, 141g for the BPL microtarp (1.4m x 1.2m), or 200g for the RAB Sil-Tarp 1 (1.5m x 2.45m).
Hopefully this gives you a brief intro to tarps, what's on the market, and why you might choose a particular item.
Once you get the tarp, there are plenty of youtube videos that will give you a very good guide on how you can rig your tarp up for your use.
Happy camping!
J
and it's easier on the pocket than some of the more expensive fabrics lol 
