Hi Megsn,

I think you write about lasso selection feature.
The Lasso selection lets you choose objects with an irregularly shaped boundary. Click, hold and move your cursor to begin the Lasso selection. Moving your cursor to the right indicates a Window Lasso, selecting only objects entirely inside the Lasso area. Moving to the left indicates a Crossing Lasso, selecting not only the objects within the Lasso area, but any objects that touch the Lasso.

Here you can find how to turn off this feature:

https://knowledge.autodesk.com/support/autocad/troubleshooting/caas/sfdcarticles/sfdcarticles/How-to...

Maxim