To play on a PC, you can use emulators such as Ryujinx or Yuzu. Simply drag and drop the extracted .nsp into the emulator.
Do you have of the archive downloaded in the same folder? Sonic Colors Ultimate (NSP)(Base Game).part2.rar
This specific file name suggests you are dealing with a for a Nintendo Switch game backup. To use this file, you need to combine it with its matching parts to extract the playable game file. How to Extract and Use the File To play on a PC, you can use