I am trying to install Baldur's Gate II: Enhanced Edition, but have two questions. First, the game downloads in two parts. How do I install them together? And also, the game comes with 5 patches. What do I do with them?

Put both parts in the same folder, then run part 1. It will automatically pick up part 2 during the installation.

You don't need the patches. Those are for people who installed previous versions.