Click on "Edit" at the top of an article. Then place double square brackets around the topic you want to link to.

For example: [[pear]]

produces the link pear

For the plural write this: [[pear]]s

which will look like this: pears

If you want to create a link to a section of an article (for example "Cultivation" of the "pear" article) place an internal hyperlink "Pear#Cultivation" separated by a vertical bar ( "|" ).

For example: [[Pear#Cultivation|cultivation of pears]]
which will look like this:

cultivation of pears