Java Help

jPortable Launcher is just a generic launcher for Java apps, it requires you to also have jPortable installed.

Here's the page for jPortable itself: https://portableapps.com/apps/utilities/java_portable

Here are the dependency packages for the online installers for jPortable 8u144 (both x86 and x64).

jre-8u144-windows-i586.tar.gz
MD5: 9e986ce96d11cb2e74a3e2ecff997cd0
jre-8u144-windows-x64.tar.gz
MD5: 7ba88a769766018e3b7c27950a758290

Make sure that the MD5 of both .tar.gz files matches as above (pulled info directly from jPortable_8_Update_144_online.paf.exe and jPortable64_8_Update_144_online.paf.exe) and that they are with the installers.

I'm not personally very familiar with JDownloader but it appears you can choose to download it as a JAR without installer (the "Other" option on the Download page), so it should be usable with a standard install of jPortable and the jPortable Launcher.

I'm not sure what you did from your description, and the page you linked is not what I would call a particularly good tutorial, but starting from nothing, what you want to do is (where X: is your drive letter) install jPortable (aka Java Portable) in X:\PortableApps\CommonFiles\Java, install the jPortable Launcher in X:\PortableApps\JavaPortableLauncher (Note: These are the default install locations if you install using the PortableApps.com Platform) and place the JAR file of JDownloader you downloaded somewhere you'll remember (e.g. X:\PortableApps\JDownloader). Then to run it you can execute the jPortable Launcher and browse for your JDownloader.jar file.

If you would rather be able to start it without having to browse for the JAR file each time, you can make a batch file to do so:
Open a text editor and (assuming you've used the same locations for everything as I described above) write this in it:

%~dp0..\JavaPortableLauncher\JavaPortableLauncher.exe "%~dp0JDownloader.jar"

Then save it in X:\PortableApps\JDownloader as JDownloader.bat, and you'll be able to easily launch JDownloader portably by executing that batch script.

Edit: Added quotes to the batch file.

Here's a PAF of an online installer for JDownloader I just made.

JDownloader Portable 32/64-bit Multilingual Online Installer

In the optional user configuration file I've added the key Java= which can be set to any location you wish JDownoader to look for JRE.

; Set custom location for JRE. ( set to directory before "bin" )
	; ie. Java=D:\PortableApps\CommonFiles\Java
	; ie. Java=X:\jre
	; Scan Priority >>
		; [1]. Java=
		; [2]. JDownloaderPortable\App\JDownloader\jre  JDownloader64\jre
		; [3]. X:\PortableApps\CommonFiles\Java  Java64
		; [4]. Locally installed Java

To upgrade JDownloader simply rerun the installer and select your bit depth accordingly; or choose both 32-bit and 64-bit version if you plan on running this on computers with both architectures.