The below links have been very helpful to me as a beginning coder:

Code Editors/Previewers

CircleJourney's TH live code preview: https://toyhou.se/6305952.-utility-live-code-editor
Cheerikola's Playhou.se code editor: https://toyhou.se/9982230.playhou-se

Off-site Resources ((not all functions will work on TH)):

"Cheat sheet" of bootstrap functions: https://hackerthemes.com/bootstrap-cheatsheet/
The official bootstrap docs!: https://getbootstrap.com/docs/4.0/layout/overview/
Display classes explanation & reference: https://mdbootstrap.com/docs/standard/layout/display/

On-site Resources:

Elithian's coding resources: https://toyhou.se/Elithian/characters/folder:881832
AviCode's misc. resources and tutorials: https://toyhou.se/AviCode/characters/folder:894384
teiyoq's misc. codes ((good as references)): https://toyhou.se/teiyoq/characters/folder:1798067
Starlipop's coding goldmine: https://toyhou.se/1099931.-coding-snippet-goldmine
BunBox's F2U snippets: https://toyhou.se/6825162.f2u-snippets-resources

General note: if the resources were not written with Toyhou.se in mind, it's likely that they list functions that aren't possible on the site ((ex. popovers/modals/etc.)).