...I have deployed my app on Shinyapps.io. Now how does one find it and use it?
If the name of the account to which you published the app is "abc" and the app's name is "def_gh" then the URL should be abc.shinyapps.io/def_gh.
If you used RStudio to publish it, you can open the program file (typically app.R if you combined UI and server functions in one file), click the down arrow on the publish icon, click the entry for the correct account, and you'll see the full URL in the dialog that opens.
You can also go to shinyapps.io, log into the account to which it was published, go to your dashboard, and find the URL there.