To check whether a rooting procedure went successfully, there are two main ways.
Root checker apps
If you prefer simpler things, you may choose one among the many root checkers. The list has been compiled by the trustworthy @Izzy, and I'll redirect you to it because I'm too lazy to reinvent the wheel today.
Manual procedure
If you don't trust in root checkers, you may also choose to install a Terminal emulator. Once you open it, enter the su
command, followed by enter. Next, enter the whoami
command, followed by enter as well, and examine the response: if it's root
, then you're rooted indeed. If it's anything else, then the procedure failed.
Off-topic footnotes
From personal experience, TowelRoot usually congratulates if the rooting procedure was successful, so it may have failed in your case. If it has indeed failed, you may try your luck with the modstrings.