Here's an article with detailed instructions: https://homeguides.sfgate.com/clean-artificial-marble-27151.html
Heat up 1 cup of white vinegar, mix in about 1/4 cup of Dawn Premium. Not the dollar store kind, because it is too thin. When mixed, pour into a spray bottle and fill with water. Shake. Spray down the grout and let it sit overnight. In the morning rinse. If you have stubborn stains, spray again. Use this mixture a few times a week. It will keep your grout and tiles clean. Also works wonders in the toilet bowl to keep hard water stains at bay. Oh you only have to heat the vinegar one time when you add the Dawn.
Any basic shower cleaner with a soft sponge should work. Once clean, you can use a daily spray like this one, ( here's an affiliate shopping link for eucalyptus mint daily spray)
grapefruit and salt