I hope I'm not breaking any overlooked rules by answering questions here. Since the forum is labeled 'Ask-a-Model!' and not 'Get-Random-Answers-From-Spammy-Members'. If so, my apologies!
For links, I'd recommend something like:
<a href="https://www.twitter.com/Luminourm" target="_blank">Twitter</a>
That would make a link to a twitter profile (in this case, mine) and would display the text 'Twitter'. target="_blank" causes it to open in a new tab instead of the current one. The above would look like this: (Note, this will not open in a new tab unless you control-click or middle mouse click, if on PC. Though you should also be able to right click it. The target="_blank" part doesn't work for the URL BBCode here, but it will work with the html code shown above.)
Twitter
You can also use an image, instead of text.
<a href="https://www.twitter.com/Luminourm" target="_blank"><img src="https://abs.twimg.com/a/1377219190/images/resources/twitter-bird-blue-on-white.png" /></a>
Sadly, they are not an approved image host for these forums, so I can't show an image example without tossing it on imgur or such, and I'm not really comfortable doing that with their logo. Here is a reference page for some images you can use specifically for Twitter, as well as their usage guidelines.
https://twitter.com/logo
I hope this proves helpful for you, and as long as I don't annoy anyone by answering questions here, I'd be happy to help with any further questions you may have. (I also hope I've described everything clearly enough.)