Please add information to explain each keyword.

The Small Basic FAQ mentions there are 14 keywords in the language:

What are the unique features of the Small Basic language?

• Size
  The Small Basic language consists of just 14 keywords.

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Here are the 14 Keywords:

Else
ElseIf
EndFor
EndIf
EndSub
EndWhile
For
Goto
If
Step
Sub
Then
To
While

And the 2 Operators:

And
Or

Within Small Basic a keyword is shown in the intellisense with this keys symbol:
 

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Examples...

If, Then, EndIf

Else

We can shorten two if..then..endif statements to be just one by using a new word, else.

If we were to rewrite that program using else, this is how it will look:

Goto

For, To, EndFor

For..EndFor is, in programming terms, called a loop.  It allows you to take a variable, give it an initial and an end value and let the computer increment the variable for you.  Every time the computer increments the variable, it runs the statements between For and EndFor.

This program prints out numbers from 1 to 24 in order: 

Step

But if you wanted the variable to be incremented by 2 instead of 1 (like say, you wanted to print out all the odd numbers between 1 and 24), you can use the loop to do that too.

While, EndWhile

The While loop is yet another looping method, that is useful especially when the loop count is not known ahead of time.  Whereas a For loop runs for a pre-defined number of times, the While loop runs until a given condition is true. In the example below, we’re halving a number until the result is greater than 1.

Sub, EndSub

A subroutine is a portion of code within a larger program that usually does something very specific, and that can be called from anywhere in the program.  Subroutines are identified by a name that follows the Sub keyword and are terminated by the EndSub keyword. Below is a program that includes the subroutine and calls it from various places.

And, ElseIf

Or