The easiest way to add a link is using append line menu:
links.png
 
There are 5 types of links you can use in your notes:

1. External link

If you need link to another website, you can just write its address and it will be automatically highlighted as a link text in your note: http://google.com/
 
If you want to write an alternative link text, you can wrap its title and link into square braces: [name][url] :
[Google][http://google.com/]
 
You can also move link urls into the separate list of references using the following notation:
[название]: адрес
For example, if you write:
[google]: http://google.com
You can use the following links:
[наш любимый гугл][google]
 

2. Relative note link

If you want to link to any of your subnotes, you can just wrap its name into the square brackets:
[][Test Note]
Or
[link text][Test Note]
 
If you want to link deeper, you can separate path with /
[][Test Note/Test Subnote]
 

3. Absolute note link

If you want to link a note somewhere outside of its parents, you can wrap a complete path from the root of the current notebook into the square brackets:
[][/Quick Start/Editing/Links]
 
If you want to link a note in another notebook, you can write its name into the path and prepend it with //
[][//Help/Quick Start/Editing/Links]
 
If you want to provide an alternative link text, you can write it in the preceding square braces [link name][note path]
[link text][/Quick Start/Editing/Links]

4. Link note by its ID

It's the most easy and persistent link, because it doesn't depend on the note path and name. You can move and rename the notes as you like, while links will remain live and valid.
 
You can see note ID as the last number in its address. You can also edit this ID in the note properties, if you want to develop clean and readable urls.
 
The easiest way to link a note by its ID is to wrap it into the square brackets:
[][32]
or
[link text][32]
 

5. Wiki-style link

It's enough to wrap note path into the double square braces: [[note path]]
 
If there is a document with this path, these braces will be replaced by the actual document link. If not, it will be highlighted with red color. When you click on it you will be asked to create the new note with this name. If any of the parent notes don't exist yet, they will be created automatically, too.
 
You can use the following note path types:
  • - [[note 1]] - links to the subnote named note 1
  • - [[note 1/note 1.1]] - links to note 1.1 subnote of note 1
  • - [[/root note/subnote]] - if path starts with / it goes from the root notes
  • - [[//Notebook/root note/subnote]] - if path starts with // it goes from the complete list of notebooks. Please note that you can link only your or shared notebooks, or the braces will not be converted into the active link.
  •  
    If you need to provide another link title, you can separate it with | sign:
    [[note path|link title]]