retinol and retinoid

Hi experts out there, I do have a question about retinol retinoid Instead of concerning about the percentage % of retinol/retinoid itself. What form /texture of retinol and retinoid product should be use in skincare routine because retinol and retinoid can come in form of toner, serum, ampoule and cream too. Should we use retinol /retinoid only in one of the skincare steps? Thanks