is it necessary to install gatsby globally code example

Example: how to install new gatsby project locally

# install new project
gatsby new [SITE_DIRECTORY_NAME] [URL_OF_STARTER_GITHUB_REPO]

# If you omit a URL from the end, Gatsby will automatically generate 
# a site for you based on the default starter
gatsby new learning

# example
gatsby new hello-world  https://github.com/gatsbyjs/gatsby-starter-hello-world