I know this is a late reply, but:
the description can be whatever you want. it shows up in the “Notes” field if you were to create the transaction manually.
selecting the property that each transaction applies to happens on import. it’s generally recommended that you include only transactions for a single property in each CSV file. then, when you import it, you can select which property the transaction applies to. if you are unable to separate the CSV, then you will want to import it to your portfolio, then manually change the property that each transaction applies to (you can use the bulk edit to make it go faster)
hope this helps