You can make a link to another wiki page simply by stating the name of the wiki page. For example, the name of this page is Markup Internal Link.

The name of a page has a special syntax known as a WikiWord. A WikiWord starts with a capital letter and has at least one more capital letter in it. Between the capitals there must be lower case letters or numbers. There cannot be two capitals in a row.

Thus:

Wiki Words
Non-Wiki Words
BobMartin Bob
RobertCecilMartin hello
ObjecT Object
NumbersLike123AreAllowedNow Butnotlikethis123

If you place a WikiWord in the markup text, but no such page exists, then you will see something like this on the page:

NoSuchWikiWord[?]

If you click on the question mark it will create that page for you, and allow you to edit it.

If the link to other pages is long, such as the link to a page in another SubWiki like <User Guide .Fit Nesse Wiki .Sub Wiki, then the link can replaced with easier to read text by using this markup:

[[text shown on screen][<LinkToOther.SubWiki]]
http://fitnesse.org/FitNesse.FullReferenceGuide.UserGuide.FitNesseWiki.MarkupLanguageReference.MarkupInternalLink
fitnesse.org
crawl=CC-MAIN-2017-39
7993
application/http; msgtype=response
sha1:YVAZ7FLMFJP3XNLBSAU5COJTWNUPGCAC
<urn:uuid:be45563b-25f1-464b-b731-f8b0201d0ead>
2017-09-23T14:44:57Z
23.23.125.155
text/html
sha1:DTSHLRBBF4HEPGHLY3ZDGLNWC5ZZMAWP
<urn:uuid:fce8d958-2af7-4de4-af81-d8600d0a7968>
http://fitnesse.org/FitNesse.FullReferenceGuide.UserGuide.FitNesseWiki.MarkupLanguageReference.MarkupInternalLink
response
<urn:uuid:f02d8862-aeb2-4213-bd7a-e119980d21df>
robots: classic
hostname: ip-10-37-236-142.ec2.internal
software: Nutch 1.6 (CC)
isPartOf: CC-MAIN-2017-39
operator: Common Crawl Admin
description: Wide crawl of the web for September 2017
publisher: Common Crawl
format: WARC File Format 1.0
conformsTo: http://bibnum.bnf.fr/WARC/WARC_ISO_28500_version1_latestdraft.pdf