how to hide columns for certain users

You're best bet would be to create and share a report to a particular user. 

https://help.smartsheet.com/articles/522214-creating-reports

With a report, you can serve them only columns that pertain to them. Do note that users who are editors on a report, must also be editors on the main sheets so its possible they could locate the original sheet and see the rows you are trying to hide from them. But if the data is not sensitive, and you're just trying to spare you user from seeing data that doesn't pertain to them, then reports would be a good way of accomplishing that.