Help creating a encrypter

1

ok so i want to create an ecrypter, not files but just messages, like “hello” int 16577. (random numbers) but the thing is, i dont know how to change the letters specifically to other characters, and i want the password to change every minute (i figured i would this by using time as a variable and somehow linking it to the pattern that changes the characters) the first problem i am encountering is telling VB to select the first letter in a string. im open to all suggestions, and no this does not serve a purpose but im its just something im trying to do