LaTeX code for HW writeups is provided as an Overleaf project. You should make a copy of the project for an assignment and write your solutions in your own Overleaf project, or download the project and edit locally on your computer if you prefer.
When homework includes programming, source code will often be provided as a GitHub template repository. Follow the link, click Use This Template then Create new repository to make your own personal copy of the repo. Then you can clone your copy and go from there. Make your repo private but add your partner if you are working with a partner.