1 - [[ Tells WikiTree that you want to create a link to something on WikiTree (can also be a category or freespace, for example)
2 - Barnes-1145 This is the profile's ID. You can find it at the top right of it's page or if you hover your mouse over a link it will display in the lower left side of your browser.
3 - | I don't know what it's called but it is used as a separator and/or sorting indicator.
4 - Brinsley Barnes This just tells the link what to display on the page.
5 - ]] Tells WikiTree you're done.
If you want to tag, or create a link on WikiTree of something off of WikiTree, like another website, it is very similar:
Ancestry.com] Instead of using the sorting/separating thingy | you use a space.