How can i make seats or benches for my deck. out of pallets?
Seats or benches or possibly even a picnic table 
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Suggested Project Book
http://www.hometalk.com/diy/build/furniture/upcycled-pallet-wood-bench-2563114
Upcycled Pallet Wood Bench
Here is a step by step instructional article about how to make a paller bench
http://www.rkblack.com/blog/posts/view/9/5-easy-steps-to-turn-a-pallet-into-an-outdoor-patio-bench
................... and here are the instructions for making a cute little daybed/patio seat with attached table
http://lovelygreens.com/2013/06/pallet-project-patio-day-bed.html
I hope these are of help to you and help add years of enjoyment and relaxation to your home. :)
Look at this. https://www.pinterest.com/explore/pallet-seating/