It’s easy af. Rose water can be used in ritual bathing, to consecrate ritual tools, to make botanicals, to cook, as an offering, to dress candles, to float candles in, to wash surfaces, in spellwork, etc.
Collect roses. Make sure they are not covered in pesticides! Store-bought roses are a no-go. Forage them from the wild or a garden. Plants have spirits and the land has eyes; ask the roses before you pluck them. And ask them to empower your water. You can also ask them if there is something you can do for them.
Pull off the petals and place them into a glass container. Do not use plastic. Jars are great, but it does not need to be a jar.
Cover the petals in freshly boiled water. Watch until the water turns pink and the petals turn pale. When the water has cooled, strain it into a glass container (jar, bottle, etc). Compost the petals if you can. Store in the refrigerator for up to 6 months.