PLEASE HELP WITH TURN AROUND TIME DATE FUNCTION, THANK YOU IN ADVANCE

I am nowhere near a Smartsheet Whiz. We have a column on our main sheet titled Create Date which we input. This is the date a work order was created. I am wanting to have another column titled TAT (turn around time) which will look at the Create Date entered and reflect how many days the ticket is open and continue to tick daily until we close the ticket. Some times the Create Date is prior to the date we actually enter it, so the TAT column would still need to reflect total days since create and running. Please help. We achieved this years ago and forgot how to do it. Any suggested automations, alerts, colors etc that could be used as TAT goes past a certian number of days would be helpful also.