Pricing a takeoff from a saved set of unit prices, matched by bid item code.
A rate sheet is a saved set of unit prices keyed by bid item code. Apply one to a takeoff and the prices fill themselves in, so pricing a job is picking a sheet rather than typing a number per line.
Choose a rate sheet in the export dialog. Every item whose Code the sheet recognises is priced, and the dialog reports how many it matched - "Auto-filled 34 of 41 items". The rest are left blank for you rather than quietly priced at zero.
If nothing matches at all it says so, which usually means one of two things: the wrong sheet, or a takeoff whose items have no codes yet.
Matching is by code, not by name. An item with no Code can never be auto-priced, however obvious its name. Filling in codes as you build the item list is what makes this work later.
Save As Rate Sheet takes the prices on the current takeoff and keeps them as a sheet for the next job. Give it a name; saving over an existing sheet asks first.
That is the usual way a rate sheet comes into existence - price one job by hand, then keep it.
A rate sheet is a snapshot of what things cost when you saved it. Re-saving after a job that had current pricing is how it stays useful; there is no automatic update, because prices coming from nowhere would be worse than prices you know the age of.