Connect Rails Application to already existing MySql Database

Hi there, I am new to Rails and really enjoying it. 
I am converting my php application to a ROR application. The app is using a MySql DB, so I want to connect the ROR application with that already created DB and want to preserve the data. php has mysqli functions, does ROR has anything similar to that ?

Help appreciated. Warm Regards.

Depending on wether you want to keep running the PHP app. If you don't, read into ActiveRecord, create your models and then write a few migrations to make sure the columns and indexes do match the naming conventions in Rails.