When the Check Engine Light comes on and keeps a steady light the computer is letting you know there is an issue with one of the sensors or sensor readings. When the Check Engine Light is flashing the computer is letting you know that something serious is wrong and the vehicle should not be driven more than a mile and then towed to prevent irreversible damage.
On vehicles that are 1996 and newer, It requires the use of a Scan Tool to extract the check engine light codes. Once you have the code you can look out the code definition and determine the best course of action for the issue. Once the repairs are completed you will need to clear the codes out of the computers memory with the Scan Tool.