to -- this keyword appears as part of other statements Synopsis for a=1 to 100 step 2 ... next a draw line x,y to a,b, View$ Description:

The to-keyword serves two purposes (which are not related at all):within for-statements, to specify the upper bound of the loop.
Within any graphical command (e.g. line), that requires two points (i.e. four numbers) as arguments, a comma ',' might be replaced with the keyword to. I.e. instead of 100,100,200,200 you may write 100,100 to 200,200 in such commands.