The & operator joins two strings together, one after the other, returning one large string.
:"Hello"&"World" "HelloWorld" :5→n :"The value of n is "&string(n) "The value of n is 5"
Appending strings is very useful when you want to display text. If you want to display more than one string on the same line, for instance with the Text command, you'll need to use & to combine the strings.
By default, & doesn't put in any separation between the strings, which can look weird: you can see this in the above example, where joining "Hello" and "World" made "HelloWorld". With multiple uses of &, you can put in any separator you like:
:"Hello"&" "&"World" "Hello World"
If you want to use & to build up a string from scratch, start with "" — the empty string.