I was also unsure about .gitignore at first.
You can simply create a .gitignore file in your project’s root folder using any text editor.
Just add the file patterns you want Git to ignore, like *.log or node_modules/. After that, stage and commit it with:
git add .gitignore
git commit -m "Add .gitignore file"
Most tools like Xcode don’t create .gitignore automatically, so you usually have to add it yourself.