Custom snippets can be accessed via menu File->Preferences->User Snippets. After that, you need to select a snippet language. In my case, this will be HTML.
To add new HTML snippet we need to add a new record in the opened html.json file.
For the Bootstrap HTML snippet I am specifying the following fields:
prefix—this name will be used by the IntelliSense and autocomplete;
description—description of the snippet;
body—content of the snippet.
Additional Functionality for Snippets
Keep in that you can use various placeholders in your snippet’s body. For example, I’m usng {$1:title} to specify that cursor should stop at this location when I’ll use the snippet. You can specify choices, tabstops, default values, and variables in your snippets.