Hey there Ayumi,
Sounds like you might have a dead digitizer - the thing that works out you're touching the screen - sadly.
I've got one suggestion that might work, and doesn't need a functioning touchscreen, but you'll need to know your Google and Samsung account passwords, and this suggestion will wipe everything on your phone's internal memory:
Step 1 - Hold the Power+Volume Down keys for 10 secs. This should perform a Simulation Battery Disconnect and restart you phone
Step 2 - As soon as the display turns off, press and hold the Power+Volume Up keys. This should load the recovery menu
Step 3 - Use the volume keys to select Wipe Data/Factory Reset, and press the Power key to select it. Use the volume keys to select Yes
Step 4 - Once complete, use the Power button to select Restart System Now. All goes well, your phone should restart into Setup and you should be able to interact with it
If that doesn't fix your touchscreen, then you'll need to contact Samsung and arrange a repair, although this should be covered under warranty as long as your display has no physical damage.
All the best, and keep being awesome,
Tom 🙂
