Hi,
So for non-calculated metrics (like orders), you can create the segment as I mentioned above...
But for calculated metrics, like Conversion Rate, so I am going to assume the metric is "Orders / UV"....
You can pull in a column for Orders, and another column for Unique Visitors.. select the two columns and right click to bring up the context menu... select "Create Metric from Selection" > "Divide"


You may want to edit the resulting calculated metric (give it a better name than what is auto generated, make it display as decimal or % and the number of decimal points, etc, and make sure the division is in the correct order...
If you need a more complex conversion.. like "Orders per UV (that actually makes an order)", then you can create a segment for "Visitors with Orders" (and make sure that you look for orders made within an appropriate time frame by adding a date range into your segment - you don't want any visitors who have ever made an order in the entire history of your site)... then you can stack that segment with your metrics, and create a calculated metric that includes the segment....