An encoder is software that lets you code your cases without code books. It provides a way to look up the codes and add the codes to your case's code list. It might also check for certain kinds of errors, like using a pediatric immunization code for an adult or coding a prostate condition on a female, or it might also check Medicare and insurer policies to be sure that the diagnoses meet medical necessity for the procedures you coded.
There are two basic types of encoders. One acts like an online code book. It lets you search for what you need, then shows you the same kind of text that you see in the alphabetic index. When you choose something there, it takes you the tabular list and shows you what you would see in your book. You can click on your choice to add it to your list of codes.
The other is a decision-tree sort of software. 3M is the most popular of that type. With that, it asks you questions to whittle down the choices until you eventually come to a code. It also can check for errors, etc.
The hitch with encoders is that if you can't code effectively with a code book, you run the risk of selecting something nuts from the encoder. It can be difficult to see what you're doing in the encoder, so you can get way off track. However, with both types you can still just type in a code number if you know it.
Don't be concerned about encoders being scary or difficult to use. They're just software and they're usually easy to pick up on with even minimal training.