The Lugaru Downloader is currently defunct, might eventually come back.
If you want to install stuff from
http://www.wolfire.com/lugaru?t=mods --
1. Open a Finder window
2. Press CMD-SHIFT-G to open a folder manually
3. Assuming your Lugaru application is at /Applications/Lugaru.app, without the quotes, type "/Applications/Lugaru.app/Data"
4. Right-click the Data folder, choose 'Copy "Data"'
5. Right-click on your Desktop, choose 'Paste "Data"'
6. Select the Data folder copy on your Desktop, hit Enter, rename it to "Data.Lugaru.backup" or something (this folder will enable you to roll back the installation to a working state in case something goes wrong after you've installed a mod or whatever)
7. Back to the Finder window
8. You've downloaded some mod, for instance "Lugaru: Temple" by Silb; let's assume the zip is on the Desktop, in a folder named "lugaru-mods"
9. Navigate to Desktop/lugaru-mods and doubleclick Temple.zip -- this extracts the contents from it and places them next to it
10. Generally, mods work by replacing files, like textures, models, maps and so on; Silb has made this easy to understand for you. If you navigate the new Temple folder, you'll notice that in "Sven Campaign", there's a
ReadMe.txt, a
What to backup.txt, and three folders named
This goes into blah (
blah being some folder name in /Applications/Lugaru.app/Data/)
11. So for each
This goes into blah folder, you navigate into it, press CMD-A to select all, press CMD-C to copy the files, navigate to /Applications/Lugaru.app/Data/blah/, and press CMD-V to paste the copied files, agreeing to questions about whether you want to replace some files
12. You make the previous step easier on yourself if you open a second Finder window, so you have one on top showing /Applications/Lugaru.app/Data/, and one on the bottom showing Desktop/lugaru-mods/Temple/Sven Campaign
13. Don't drag-and-drop, don't right-click+copy / right-click+paste; OS X does not expose pasting in right-click menues if the target location is in a .app package. Really use CMD-C and CMD-V
14. Other mods sometimes have the Data/ folder inside and you can just paste the contents into the /Applications/Lugaru.app/Data/ folder; you'll be fine
15. If something breaks, then replace the Data/ folder inside the .app with your backup
16. All this can end up being rather involved, that's why the Lugaru Downloader exists in the first place
17. This space intentionally left blank
Good luck
Edit: If you're scared about breaking your Lugaru installation in some way STILL, then you can simply copy / paste the whole Lugaru.app to somewhere before fiddling with its contents; that way, you can also parallely play the original version, and the modded version, as an added bonus. Thinking further, you could of course copy / paste a new Lugaru.app version, then mod it, then eventually have all mods available on doubleclick at all times without all the hassle; but that takes a lot of copypasting. I'd recommend doing that successively (building a new modded installation when you want to try a new mod).
You can also rename .app packages; so you'd probably like to name the Temple-modded version "Lugaru_Temple.app". And it doesn't matter where the .app is, so maybe you want to make a Lugaru Mods folder on your Desktop, and drop the modded versions there. Just in case you're as OCD as I am sometimes.