Cleaning a computer keyboard is easier than you might think.
Turn off the computer. You can seriously damage your computer via the keyboard using liquids. Unplug the keyboard from the computer (another safety measure).
Using a damp cloth you can wipe down the outside case of the keyboard. Water is usually good enough but you could also use rubbing alcohol. Don’t use spray cleaners unless you spray onto the cloth and then wipe. I would recommend the rubbing alcohol only because it cleans better than just water and even if it splashes onto the keyboard unseen it will quickly evaporate.
Cleaning the inside under the keycaps requires the removal of the keycaps using a keycap removal tool. Once removed you can turn the keyboard upside down and shake loose most of the crumbs. With the keycaps removed you can easily clean them thoroughly using rubbing alcohol or water and mild detergent. If you want, you could place them in cheesecloth or a mesh bag and run them through the dishwasher on the top shelf.
Allow keycaps to dry and replace onto the keyboard.