I don't know if you want to load your levels from text files and allow users to modify them but this is my example of AmigaBASIC code for reading in text from file, I use a slight variation on this for reading in highscores in my next game. You might be able to modify it to use in Blitz Basic if you want to load your levels from text files and allow users to modify them.
Example of file TOH
100,90,80,70,60,50,40,30,20,10
' CODE FOR IN PROGRAM
Code:
' ARRAY TO STORE SCORES
DIM SCOREZ (10)
' OPEN FILE "TOH" FOR READING
OPEN "TOH" FOR INPUT AS 1
' LOOP TO READ IN AMOUNT OF SCORES
FOR COUNT = 1 TO 10
' READ INPUT FROM OPEN FILE 1 INTO ARRAY
INPUT# 1, SCOREZ (COUNT)
NEXT
' CLOSE FILE 1
CLOSE 1