Basically, it's "download->connect devices->install", there will be extra steps depending on your Windows version and updates.
Main File and Pre-requisites:
W8 and below: Pre-requisites (you can skip these and download using the promp message in the setup)
∙ Microsoft .NET Framework 4.5
∙ Microsoft Visual C++ 2010 Redistributable Package
∙ Microsoft Visual C++ 2013 Runtime
∙ Microsoft DirectX Runtime (Windows XP and Windows7 Old SP) - Requires internet connection
∙ Xbox 360 Controller driver (WindowsXP or W7 Old ServicePack)
Download the main file and install using the default settings or disable what you don't need, specially those unstable components.
Just don't forget to check the main components, SCP toolkit monitor (legacy) and the "SCP Toolkit Bluetooth Pair Utility" to be able to pair your DS3 controller to your Bluetooth dongle.
and (if you want/need) download the pre-requisites as well and install them all.
If you haven't downloaded and installed the requirements from Microsoft, download them using the prompt message in the setup but it's better to get them directly from Microsoft's website.
Plug all the devices you have (PS3, PS4 and Bluetooth Dongle) then open the "ScpToolkit Driver Installer.exe" from then SCP_Toolkit_setup's installation directory.
Check the necessary options depending on your PC, Bluetooth Dongle and DS3/4's device ID.
The image is pretty much self-explanatory, just check what you need. You can even disable the bluetooth driver to install just the PS3 Driver for "Wired connection-only setup".
Check "Install Bluetooth Driver", "Install Xbox 360 controller Driver", "Install DualShock 3 driver" and Select the proper devices from the drop-down list.
You can find the device ID from the Device Manager (start->search: device manager) and look for Bluetooth devices, Game Controllers, Human Interface Device and "Unknown Devices".
(Note: installing the bluetooth driver will disable your bluetooth device's ability to connect to bluetooth devices other than your PS3 controller.)
Uncheck "Install DualShock 4 driver" if you didn't have a PS4 controller, uncheck "Install Bluetooth Driver" if you didn't have a compatible bluetooth dongle and Uncheck "Install Xbox 360 controller driver" if you already installed it before.
When everything's done and correctly set-up, click "install".
Wait until the installation is complete (until "install" is clickable again), close the installer and restart your PC.
After booting, a "Ds3Service" should be running in the "services" after a few minutes.
You only need to pair your DS3 Controller's MAC address to your BT Dongle's MAC address using the "SCP Toolkit Bluetooth Pair Utility" from the SCP_toolkit directory
To find the Bluetooth address, Open SCP toolkit monitor (legacy) and double click it from the notification bar (it's the Host Address).
Now, plug your DS3/PS3 Controller to your PC and open the pairing tool, next copy the Host Address (ex. 00:11:22:33:44:55:66) and paste it to "SCP Toolkit Bluetooth Pair Utility"~'s input box, then press ok/pair.
Your DualShock3 controller should work wirelessly by now.
1. If Ds3Service failed to run during startup most of the time: Go to Services (start->seach: services), find & double-click "SCP DSx Service" and change Startup type from "Automatic" to "Automatic (Delayed Startup)" then press ok.
2. If your Bluetooth connection didn't work, Ds3Service might be "stopped" not "running" (refer to troubleshooting no1); or your Bluetooth Dongle might not be compatible with the driver (here's the compatibility list)
But not all compatible devices are listed, mine for example.
3. If nothing worked (including the DS3 controller - connected via USB), double-check the pre-requisite files if you have the exact versions specially the first three in the list (above).