What are all these streaks and lines? When I try to use the Finder Scope, it doesn't know about them.

The streaks and lines that appear in WWT, but are not astronomical objects, are usually imperfections in the imagery of the telescopes. Many line segments are the result of things like meteors, aircraft, and satellites. Meteors usually show up as lines with pointy ends and a brighter middle, and are sometimes green. Satellites can present as dashed blue lines. Aircraft lines are usually fairly solid and uniform, but sometimes wiggle a bit from turbulence in the air. White lines are often "seams" between images.