what's the difference between joke, play on words, wordplay and pun?
can you give me some examples too? thanks.

Question

Answer

The dictionary is a useful tool to learn what words mean:
1. http://www.merriam-webster.com/dictionary/joke
2. http://www.merriam-webster.com/dictionary/wordplay
3. http://www.merriam-webster.com/dictionary/pun
4. http://www.merriam-webster.com/dictionary/play%20on%20words

2, 3, and 4 can mean the same.  Thousands of puns can be found via an Internet search:  
A. http://onelinefun.com/puns/

B. https://search.yahoo.com/yhs/search;_ylt=A0LEVrdq9bBX3WYAN6gnnIlQ;_ylc=X1MDMTM1MTE5NTY4NwRfcgMyBGZyA3locy1tb3ppbGxhLTAwMQRncHJpZANPMWl3YlNyelM5cWh6bkdEX0pIbjRBBG5fcnNsdAMwBG5fc3VnZwMxMARvcmlnaW4Dc2VhcmNoLnlhaG9vLmNvbQRwb3MDMARwcXN0cgMEcHFzdHJsAzAEcXN0cmwDNARxdWVyeQNwdW5zBHRfc3RtcAMxNDcxMjE1MjAx?p=puns&fr2=sb-top&hspart=mozilla&hsimp=yhs-001

1 is different.  Thousands of jokes can be found via an Internet search:

C. https://search.yahoo.com/yhs/search?p=jokes&ei=UTF-8&hspart=mozilla&hsimp=yhs-001