Font Awesome (Icons):
https://fontawesome.com/
Google (Anything):
Googling will get you very far, google "[what you're looking for] HTML Bootstrap", links in the search results from stackoverflow.com and www.w3schools.com usually have the answers. You can also search questions about ToyHou.se in Google and find ToyHou.se forum posts discussing what you're looking for.
Inspect Element (Viewing Code):
Right click or developer tools in browser menu to access. You can see any page's code (TH's site coding, user content, and some other sites use Bootstrap). Just don't use it to steal and reupload personal or P2U codes because that's sucky, there are plenty of F2U codes you can use instead.
I added some basic codes below (for personal reference and anyone interested), do not credit me for these. I will add more eventually, let me know if there are any specific codes you're looking for (check Bootstrap manual for more).
<div class="card mb p-3">Text</div>
<div class="card mb bg-faded p-3">Text</div>
<div style="background:#000000; padding-top: 12px; padding-bottom: 12px;padding-left: 12px;padding-right: 12px;">Text</div>
<table style="width: 100%;">
<tbody>
<tr>
<td style="width: 100%; background-color: rgb(0,0,0); padding: 12px;">Text</td>
</tr>
</tbody>
</table>
Solid color:
<div style="position: absolute; top: 0px; bottom: 0px; left: 0px; background-color: rgb(0,0,0);width:100%; z-index: -1;">.</div>
<div style='position: absolute; top: 0px; bottom: 0px; left: 0px; background: url("image"); width: 100%; z-index: -1;'>.</div>
<div style='position: absolute; top: 0px; bottom: 0px; left: 0px; background: url("image"); width: 100%; background-attachment: fixed; z-index: -1;'>.</div>
<div style='position: absolute; top: 0px; bottom: 0px; left: 0px; background: url("image");background-size:cover; width: 100%; z-index: -1;'>.</div>
<div style='position: absolute; top: 0px; bottom: 0px; left: 0px; background: url("image");background-attachment:fixed; background-size:cover; width: 100%; z-index: -1;'>.</div>
<div class="p-3">Content</div>
<div style="padding-top: 12px; padding-bottom: 12px;padding-left: 12px;padding-right: 12px;">Content</div>