Possibly something similiar to this (but you may want to use some sort of array)
rem Get all of the strings to use
test$="This is the first test string"
test2$="DarkBASIC is fun!"
test3$="I like to eat popcorn"
rem Save the strings to file
open to write 1,"filename.dat"
save string 1,test$
save string 1,test2$
save string 1,test3$
close file 1
rem Load the strings
open to read 1,"filename.dat"
read string 1,stringtest$
read string 1,stringtest2$
read string 1,stringtest3$
close file 1
rem Print results
cls
print stringtest$
print stringtest2$
print stringtest3$
I hope that is along the lines of what you wanted