One thing to be aware of is that Clarity has not compressed/optimized any of the images used in their widget, so it will slow down your page speed. Below is page speed report from google:

Optimize the following images to reduce their size by 17.4KiB (55% reduction).
Losslessly compressing https://clarityfm-assets-production.s3.amazonaws.com/…mex-768ffd0e7255faa690c1a05d66a71448.png could save 2.8KiB (63% reduction).
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Losslessly compressing https://clarityfm-assets-production.s3.amazonaws.com/…ver-f97844e5cad454428ab9b4cee226d0f8.png could save 2.7KiB (71% reduction).
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Losslessly compressing https://clarityfm-assets-production.s3.amazonaws.com/…pay-52c4da6e5e73c3350ee072b86209a145.png could save 2.1KiB (34% reduction).
Losslessly compressing https://clarityfm-assets-production.s3.amazonaws.com/…ess-4c9b561c55be9d52d5a47a55dcbbc287.png could save 1.2KiB (41% reduction).
Losslessly compressing https://clarityfm-assets-production.s3.amazonaws.com/…irm-4b67ba05679414b43b9b070197abfb63.png could save 1KiB (50% reduction).
Losslessly compressing https://clarityfm-assets-production.s3.amazonaws.com/…est-9ab9d850e814c7635c6281b5a0a26d07.png could save 893B (57% reduction).
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Losslessly compressing https://clarityfm-assets-production.s3.amazonaws.com/assets/modal/clarity.png could save 670B (50% reduction).

Minifying https://clarity.fm/…rce=blog&display-rate=null&js_auth=false could save 1KiB (3% reduction) after compression.

Minifying https://clarityfm-assets-production.s3.amazonaws.com/…ests-efe948239fec843153d6e50fc146e446.js could save 2.2KiB (3% reduction) after compression.

Compressing https://static.wepay.com/min/js/tokenization.v2.js could save 7.8KiB (68% reduction).

You can embed the Clarity widget using this code:
http://clarity.fm/me/widget

Dan is right, that's where you start. Here's a guided answer if it helps.
https://www.youtube.com/watch?v=-oijCV-Klao

HI

So how do I modify the width?

And I"ve got a self hosted blog...so you said it only works on a wordpress.org blog?

I have tried it on my typepad blog: http://anina.typepad.com/anina/

doesnt seem to work well...unless you can modify the size of the iframe.

On my wordpress blog, doesnt work at all. doesnt even show up....

http://china.360fashion.net/

Thats a pity.