I realize that this question may be borderline bannable because it's asking for suggestions on tools, but it will really help newbies. This online tool allowed me to play around with hashes and to really understand them at a deeper level: http://www.fileformat.info/tool/hash.htm
I can't find a similar tool (that works) for ECDSA cryptography where I can play around with public and private keys, and do digital signatures on messages, and test signature verification.
I've found these 2 sites that claim to do this but didn't work for me:
UPDATE: Great suggestions below. Some tools I found:
for hashing: http://www.fileformat.info/tool/hash.htm
generating public private key pairs and decrypting ciphers: https://8gwifi.org/rsafunctions.jsp
Generating EC public private key pairs and signing Verifying the Message https://8gwifi.org/ecsignverify.jsp
generating public private key pairs and testing signing: https://kjur.github.io/jsrsasign/sample/sample-ecdsa.html