Astringents or toners are meant to be an extra step after cleansing to remove any last traces of cleanser and/or oil, seal the skin, and prep it for additional products like foundation or moisterizer. "Astringents" are usually for oiler skin types, and almost always include alcohol. "Toners" tend to be for dryer skin types, and contain emollients to keep the skin conditioned and soft.
There's no rule saying you have to use a toner or astringent as part of your daily routine; it's more about preference.
It's smart to look for a product without alcohol, which can irritate the skin. Neutrogena makes an alcohol free toner, as do Nivea and Aveeno. Check www.drugstore.com
for details. If you have oily skin, look for a product without additional oils.
A lot of excess oil can be taken care of with daily cleansing (two or three times a day with a gentle cleanser, like Clean and Clear Sensitive Skin Foaming Face Wash) and a mask or pack every few days. Plain milk of magnesia (unflavored) makes a great oil absorbing face mask. See the link below:
Hope this helps!