Getting Started
Installing Jace
In order to use Jace, you must first have a Java 1.6 or higher runtime installed. The Oracle (formerly Sun) Java and OpenJDK should both be suitable. You only need the runtime edition (JRE). The development kit (JDK) is only necessary if you plan to do anything with the emulator's source code.
Oracle Java download location: http://www.oracle.com/technetwork/java/javase/downloads/index.html
Open JDK home: http://openjdk.java.net/
If you're using Mac OSX, you should look for Java under software updates in /Applications/Utilities/Java (note: I don't have a Mac and have no way of verifying this. If someone wants to shoot over a screenshot or some description of this I'll post it here. Thanks!)
After you have Java 1.6 or higher installed, next you'll need to download "jace.jar" from the sourceforge page: http://sourceforge.net/projects/java-ace/
Depending on if Java is integrated in your desktop or not, you might be able to either double-click on the jace.jar file to start it, or you might have a context menu option if you first right-click (or option-click if your mouse is insufficient at performing right-clicks). You should have an option labeled something like "Open with Java Runtime" or similar. If you're a Linux user, you will most likely have to set the execute bit (+x) before this will work.
If all else fails, drop to a command propmpt and type the following from the directory where jace.jar resides: "java -jar jace.jar"
Using Jace
Assuming that you got the Jace window up, you should now hear a beep and see "Apple //e" at the top of the window. You should also see some help text in the screen as well. The on-screen instructions summarize some basic keystrokes, but the most important of which is F4 which opens the configuration window. The configuration window is arranged in two panels. The left panel shows a summary of all configurable objects, and the right side lists all configuration settings available for the currently selected object. Note that settings are not effective until the Apply button is clicked. If you click on another configuration object on the left after changing settings, you should see the previous object indicated in italics to inform you there are settings that are not yet applied.
At the present, there are many different keys that map to the Reset key of an Apple //e. F12, Pause/Break and Page Down all will trigger a reset condition as long as the control key is pressed. Pressing these keys without pressing control will have no effect, just as a real Apple //e acts. You can warm-start (reboot) the emulator by pressing Ctrl + Left ALT + Reset (where reset is one of the aforementioned keys). If you press Ctrl-Reset during boot, you should get a basic prompt (which is a ] with a blinking square cursor). If you type the following and press Enter: PRINT "HELLO WORLD!" Then it should respond by printing out the same message on the next line and so on.
If you are unfamiliar with Applesoft Basic, you can get more information here: http://en.wikipedia.org/wiki/Applesoft_BASIC
From the basic prompt, you can boot a disk directly with PR#6 or boot a hard drive image with PR#7 -- assuming of course that you've already inserted an image in the configuration screen.
Configuring the emulator
When you press F4, a window will pop up showing the structure of the emulator on the left. When you click on one of the items on the left, configuration options for the selected device will open on the right.
Click on "Computer (Apple //e)" to see what cards are inserted in the computer. A standard configuration is to have the mouse interface in slot 4, a floppy controller in slot 6 and a mass storage controller in slot 7.
After reconfiguring cards, press APPLY and you'll see the section under "Motherboard" update to show your current card configuration.
Clicking on the Disk ][ Controller and Mass Storage Controller cards will let you select disk images. You can also do this with F1, F2 and F3 but those changes won't be saved in the configuration. If you change disk images in the configuration screen and click SAVE, then JACE will start with these disks inserted automatically next time. This might not be too useful for disk images, but it is probably handy for hard drive images.
If you go to Motherboard and set max speed, you might have to select something else on the left before clicking Apply in order for max speed to take effect. There's an odd bug in the UI I haven't sorted out. If this is a bother, you can also use the commandline options to ensure that maxspeed is enabled at start (see the configuration section for more details)
Other configuration options are described (as well as command-line configuration) on the configuration page link above in the site navigation.
Where to find software
You can find disk images (as well as some hard drive HDV and/or 2MG) all over the web. If you download a compressed file (gz or zip extension) then use a decompression utility (such as winzip) to extract the actual disk image before trying to use it in JACE. Here are a couple of my favorite places:
Various games I like to play:
Flobynoid: A MUST if you're an Arkanoid or Breakout fan Note: Use MOUSE for an awesome gameplay experience
Transylvania: A great graphics adventure and a rare use of the "Mixed RGB" double-hires graphics mode
Chipwits: Program your robot to survive different environments and see how long it lasts. Also supports mouse. Read tip above for setting MAX SPEED.
Asimov: ftp://ftp.apple.asimov.net/pub/apple_II/images/
Note: Some titles are compressed in zip or gzip format. You will need to decompress these first to use them in Jace
Virtual Apple: http://virtualapple.org/: A very well-organized site. If you install the ActiveGS plugin, you can play the games right from your browser! You can also download disk images here.