Can you use us 1 dollar silver certificate as regular money?

Silver certificates have never been withdrawn or demonetized so they're still "regular money".

You can't exchange them for silver metal anymore; that practice was abolished in the 1960s. You can spend them at face value but that's probably not a good idea. Most silver certificates are worth more than that to a collector - sometimes only a small amount, sometimes a whole lot more. For example, a 1957 US $1 silver certificate in average condition will generally only bring $1.25 to $1.75 on the collector market. However if you have a much scarcer 1928-E $1 bill, it might sell for $200 to $500.