config.txt is the miner configuration file. You can use it to set the miner parameters instead of specifying them in the command line or .bat file. epools.txt and dpools.txt are where you can specify failover pools in case the main pool go down. If the main pool specified in the configuration file goes down, the miner will switch to the other pools listed in epools.txt (for ETH) and dpools.txt (for the secondary coin when dual mining).