Enter this in the search box along with your search terms:

Get all gists from the user santisbon.
user:santisbon

Find all gists with a .yml extension.
extension:yml

Find all gists with HTML files.
language:html

Find all gists with a ".bash_profile" file.
filename:.bash_profile

Excludes all results containing your search term.
NOT

Find gists with greater than 100 stars.
stars:>100

Include anonymous gists in your search.
anon:true

Search all forked gists for results.
fork:only

Find gists containing a file larger than 1000kbs.
size:>1000

Find all gists with the word fetch by santisbon updated or created recently.
fetch user:santisbon updated:>2019-01-01 fetch user:santisbon created:>2019-01-01

Full code search:
https://help.github.com/articles/searching-code/

Searching:
https://help.github.com/en/github/searching-for-information-on-github/searching-for-repositories#search-by-when-a-repository-was-created-or-last-updated