Hello

Is my understanding below correct?:

No.

1. For the 1st forum, I do the installation in a normal way.
(e.g. www.mydomain.com/1st-forum/)

Yes.

2. Then, I copy the whole directory, and re-name for the 2nd forum.
(e.g. www.mydomain.com/2nd-forum/)

No, do not copy the installation. Install a second forum independent from the first one in the other directory (in directory 2nd-forum) with different table and cookie prefixes.

3. I "manually" modify the db_settings.php file as explained by Auge for 2nd-forum.

Yes. Do this after isntalling the second forum with its config/db_settings.php.

4. I "manually" copy tables from 1st forum, and with another table prefix, past the tables in the same database for the 2nd forum.

No. the install script of the second forum created the tables automatically. You'll have two sets of tables for each of the installations in your database. No neede for copying any tables.

If you change any table name in the db_settings.php to a table name of the first installation, the second forum will use the data from the specified table inst4ead it's own.

Even if my understanding is correct, both directories 1st-forum and 2nd-forum contain the whole script, so it is not multi-site, but just sharing the same database...?

Both forums will share the database tables you specified to share in the db_settings.php. Sharing all tables is pointless, because this would be one forum (under different URLs).

Tschö, Auge