The task itself is actually not too bad and gives you ample places to prove what you know, from getting user entry to working out a suitable way to store the values in variables (HashMap perhaps vs a lot of variables for each combination…). I also like the extension activity of getting the total number of occurrences of symbols throughout the words - This is the basis for a basic cipher text attack and with the correct english language letter distribution tables (http://rumkin.com/tools/ cipher/frequency.php).
I think so long as you know how to display text, get input from the user and can work out a rudimental form of loop to handle the “menu” system as such (add pairing, delete pairing etc) then you will be fine…
There are a few different approaches to the rest of the tasks but keep going.