Navicat will make assumption on the field types and length in the source table. You are allowed to choose your desired type from the drop-down list.
Hint: For importing multiple tables, select the other tables from the Source File drop-down list.
If you are importing your data into the existing table, then you might need to map the source field names manually to the destination table or just control-click and select Smart Match All, Direct Match All and Unmatch All from the popup menu for quick mapping.