How to Make A Shop
If you simply want to buy goods quickly, just use /shop. But, if you want to rival server pricing and try to sell goods from your own shop, you can do so using a chestshop. Doing this is very simple.
Place a sign 1 block away from a chest (like above it, for example).
Leave the first line blank.
For the second line, put the number of items per purchase (for example: 64).
The third line will then be the price you are going to sell the items for. This is the format you will use: B <price>:<price> S. For example, B 6:4 S. The B side is how much people will purchase items for, and the S side is how much people can sell the items to your shop for.
The last line of the sign is the item ID. So to sell stripped birch logs, you'd write stripped_birch_logs.
To make sure you are buying/selling items at a fair price, do /worth on the item you are holding to see how much it is worth.
Note: You can also use a tradeshop!