Question: 1. How to make slf4j use few implementations `(appenders)` if a want to log to console AND file both? (something similar to configuring log4j using loj4.properties file)
2. How to do my own slf4j impl? Just implement interface and it will be found on the classpath automatically?

Answer: 
SLF4J just a simple facade: *"The Simple Logging Facade for Java or (SLF4J) serves as a simple facade or abstraction for various logging frameworks, e.g. java.util.logging, log4j and logback, allowing the end user to plug in the desired logging framework at deployment time. "* (From <http://www.slf4j.org/>)

So you need an implementation too which could print or save your log messages. There are some options: <http://www.slf4j.org/manual.html#swapping> I'd choose [Logback](http://logback.qos.ch/). Check the [logback manual, Chapter 4: Appenders](http://logback.qos.ch/manual/appenders.html) also.
1. You confuse here implementations with appenders. An **appender** is a physical logging target (a file, console, etc.) and it's a term from log4j or logback, which are slf4j **implementations**. SLF4J does not know about appenders.
2. SLF4J is designed to work with one implementation at a time. If you need to use many, you'd have to implement `org.slf4j.impl.StaticLoggerBinder` yourself, and put it in the classpath as the only class with this name, and route your logging inside this class. I'm still not sure, though, if this is what you want.