On a Linux PC open the "Terminal"

Create a new folder in your "home" directory and go there:
mkdir ~/myapps
cd ~/myapps

Create a file called "helloworld.lms":
gedit helloworld.lms

Key in the following source code:

vmthread  MAIN
{
  UI_DRAW(FILLWINDOW,0x00,0,0)                  //  Clear screen
  UI_DRAW(TEXT,FG_COLOR,10,50,'hello world')    //  Write "hello world" at 10,50 (X,Y)
  UI_DRAW(UPDATE)                               //  Show the stuff
  UI_BUTTON(WAIT_FOR_PRESS)                     //  Wait for button press
}

Save and quit

Navigate to the "lmsasm" folder and

Compile the file with following command:
java -jar assembler.jar ~/myapps/helloworld

A file called "helloworld.rbf" should appear in your "~/myapps" folder.
Move your "myapps" folder to the root directory on a SD card.
Insert the SD card into the EV3 slot.
Navigate to the "SD_Card/myapps" folder on EV3 and start "helloworld"