They were buying it for more than you could get at your local smith, which is completely silly. The esp file adjusts the buying price from NPCs who have a dialog option to buy ore and wood.
Chopping wood is done the same way and yields 10 firewood per hour. When you have enough, just step back or press e to stop mining. Your character is rewarded by a variable number of ore, depending on the metal: In order to mine ore, click on it and push the wait button to advance time (or look at your screen for an hour, it'll work too). For a vanilla install it has only advantages and is intented for players using realism mods adding the need to eat, sleep, etc.
This mod allows a player to mine and chop wood in a more realistic maner, by needing to spend time working. The player can clean a mine in a matter of minutes, which is good for gameplay but not for immersion. In vanilla Skyrim, mining is nearly instant for the player, while NPCs strike the ore veins endlessly.
