This is a good question... I'm not sure if this is a good answer. Maintain can mean to keep things in the same condition. You "maintain" things like roads, machines -- you can think of "maintenance" -- keeping something in good shape. A plane can also maintain its altitude (keep the same height), or when baking something, maintain the same temperature. To "retain" something is to not lose it. It can sometimes mean the same thing as maintain. To retain an employee is to make sure the employee doesn't quit. A "retainer" can also be the service fee for a company or service provider (a retainer fee to a lawyer or banker). It can also mean to hold something -- like the soil retains water (it holds water). I hope that helps... There are better examples if you just search on Google. Just type "define:maintain" or "define:retain"

Maintain means keep something in good condition, look after something. Retain means to keep something, for instance Arthur is responsible for maintaining the files. and Arthur retained tickets with him.