Singleplayer/Client: 1. start with fresh .minecraft folder 2. drag files in "add to jar" into your minecraft.jar 3. delete META-INF 4. drag all folders and files in "add to .minecraft" merging folders and overwriting files if necessary 5. close everything open minecraft and play
Server: 1. port forward (or you can use hamachi) 2. create a new folder 3. drag all files into that folder 4. open run.bat 5. server should start