TinkerCAD

Whenever I zoom now, it zooms towards my mouse, and it didn't used to do that. Is there a way to turn that off?

Since few days I star to have problems in Thinkercas impossible to split or join STL imported from Thingiverse or other. When I select to modify, the group Split Join, does not activate. Someone can solve me this problem?

I found that some stl files that arent made in tinkercad have gaps and corruptions when imported. Some things on thingiverse and models i make in blender are messed up in tinkercad. Any way to solve this?

I am a newbe to 3D designing. The guy that was teaching me how to design things in 3D had to leave. His company transferred him to a new office in an other town. Now I have dabbled in Windows 2D paint. And I know how to take files in Thingiverse, download the files into Cura, Go through the setup routine and start the print. I have successfully 3D printed a few things already.

I think I am in, what I think is, TinkerCAD's main design page with a blank table. On the right is a bunch of blocks, cones, tubs and so on. On the left there is a bunch of shapes and 2 arrows 1 pointing left and 1 pointing right that are grayed out. Above that is "Fantastic Maimu Rottis" That I can't make heads or tails of it. I need some kind of manual "in an English format" that starts out with the basics. Since I have done some stuff in Win 2D paint. I hope that gives me somewhat of an edge.

Hello Guys,
I am need of some help creating a screw cap. Can this be created in TinkerCAD?
Could someone help me with this?

Thank You