It's pretty common for stock solutions to be made in ethanol or DMSO. Both of these can be toxic to cells, so it's best to dissolve your compound of interest in the minimal amount of DMSO (or ethanol) possible, in order to minimize solvent cytotoxicity. You'll then want to dilute the compound into your cell culture media and can do a serial dilution with media to get lower and lower concentrations. So, determine the highest concentration you want, first, make the appropriate stock, and dilute down from there in whatever increments are most appropriate for your compound - two- to ten-fold dilutions are pretty common for each step.

thank you so much Ross that was helpful :)