You import TD Ameritrade trades into a trading journal by either auto-syncing through TD's API or exporting a transactions CSV and uploading it manually. To export manually, log into TD Ameritrade, go to My Account, then History & Statements, click the Transactions tab, and click download.
Note that TDA trade history is no longer available on TD Ameritrade's website and historical trade history is now obtained from Schwab.
For complex options strategies, the thinkorswim Account Statement export gives more complete data than the basic transactions file.