How do i import certain files into Unity?

The files are .tri, .curJ , .sat, .stp, and .silo. How can i import one if not all of these files

Just go Assets → Import New Asset and select the file you want to add to your project.
Or you can go to your Documents → → Assets and drag and drop your files in there

Unity does not support this formats. see this link:

unity supported formats

but you can convert some files to obj in here