A wallet transfer transaction is when you transfer coin from one wallet to another hence there is no net change in position. However these will be captured in the transaction import hence the need to account for them.
On this screen it is possible to unclassify existing transactions; this will preserve the main information of the transaction and will allow you to reclassify it as a different type of transaction without needing to re-enter it. i.e. Fees -> Unclassified -> Trade.
You can auto use the auto-value feature for looking up historic prices.
For more information on auto-value click here.