Snippets are script templates. In postman we can create scripts in multiple locations such as collection level, folder level and request level. Scripting can be done as pre-request scripts and tests.

Collection level scripts

Click on more option on the collection -> Edit

Same as we can add folder level scripts as pre-request scripts or tests in folder level by clicking more options on folder -> Edit and in request level by by clicking on more options request -> Edit

And in the right side of the window we can see quick scripts such as to get variables and set environments in different levels.