Solaris is available in 3 different plugin versions: 

VST2.4 32-bit: Solaris.dll
VST2.4 64-bit: Solaris (64).dll 
VST3 64-bit: Solaris (64).vst3 

Simply place the plugin file in your appropriate folder, and scan the plugin in your DAW.

If your DAW or Host does not find the plugin, cannot load it, or otherwise shows an error of some kind, you might be missing the Visual C++ Redistributable Package 2013. Please download and install vcredist_x64.exe for the 64-bit, and vcredist_x86.exe for the 32-bit version:
https://www.microsoft.com/en-us/download/details.aspx?id=40784

If that still did not help, there might be other packages missing on your system. You can try installing an all in one package with all the different Redistributable Packages available:
https://www.techpowerup.com/download/visual-c-redistributable-runtime-package-all-in-one 

Enjoy!
Adam Szabo
