firstly, is there any particular reason you didn't download the latest version (2.4.3)?
Here are the instructions from the doc 'release_notes.txt' that comes with the download. Should be pretty much the same for 2.3.0 (don't have a copy at hand), look for the one in your download.
Quote:
Installing XOOPS
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1. Copy the content of the htdocs/ folder where it can be accessed by your server
2. Ensure mainfile.php and uploads/ are writable by the web server
3. For security considerations, you are STRONGLY encouraged to move directories "/xoops_lib" (for XOOPS libraries) and "/xoops_data" (for XOOPS data) out of Document Root, and change the folder names.
4. Make the directory xoops_data/ writable; Create (if not already present) and make the directories xoops_data/caches/, xoops_data/caches/xoops_cache/, xoops_data/caches/smarty_cache/ and xoops_data/caches/smarty_compile/ writable (permission 0777 on Linux).
5. Access in your Web browser the folder where you've installed the htdocs/ files to launch the Installation wizard 6. Follow the instructions