I have a tutorial for RetroArch for Windows as well.
The default setting is “ 2 - Safe (faster)”. Look towards the bottom left for this slider shown below: First, access the video plug-in settings by going to Config > General Settings, as shown below: PCSX2 makes adjusting game performance very easy with a simple slider. Maybe if you're on a Windows tablet or a budget laptop, you'd need to make use of the speed hacks if you find that games are running slow. The default settings are fine for most people. With today's computers you don't need to use PCSX2's speed hacks.
Don't place the BIOS files in a sub folder within the BIOS folder!
It's very important that you match the above screenshot on your end. Download the BIOS if you haven't already, unzip it, and drag its contents to the BIOS folder. Note the path where the BIOS folder is located.