I have this file which i got from my friend but when itry to add it to the projects in unity hub, it says that the project is not valid.

What he sent you is a built project, not the project itself.

If he intended to share the project with you, you’ll have to ask for the source files. The folder structure will then look something like this:
193888-proj.jpg

Thank you. That makes sense. Is that the reason there are so many .dll files ? Because the project is already compiled? Thanks for the help, I am new to unity. So much to learn @asafsitner