先下載檔案並解開，我建議放在 C:\letsencrypt，語法如下

Let's Encrypt (Simple Windows ACME Client)
Renewal Period: 60
Certificate Store: WebHosting

ACME Server: https://acme-v01.api.letsencrypt.org/
Config Folder: C:\Users\Administrator\AppData\Roaming\letsencrypt-win-simple\httpsacme-v01.api.letsencrypt.org
Certificate Folder: C:\Users\Administrator\AppData\Roaming\letsencrypt-win-simple\httpsacme-v01.api.letsencrypt.org
Loading Signer from C:\Users\Administrator\AppData\Roaming\letsencrypt-win-simple\httpsacme-v01.api.letsencrypt.org\Signer

Getting AcmeServerDirectory
Loading Registration from C:\Users\Administrator\AppData\Roaming\letsencrypt-win-simple\httpsacme-v01.api.letsencrypt.org\Registration


Authorizing Identifier exammple.com Using Challenge Type http-01 Writing challenge answer to C:\fms\tymetro\.well-known/acme-challenge/gJ0q7Vvdas23dAoAlTh8wTvxgmEb7f9ZIIsB3anRliXQ
 Answer should now be browsable at http://exammple.com/.well-known/acme-challenge/gJ0q7Vvdas23dAoAlTh8wTvxgmEb7f9ZIIsB3anRliXQ
 Submitting answer
 Authorization Result: valid

Requesting Certificate
 Request Status: Created
 Saving Certificate to C:\Users\Administrator\AppData\Roaming\letsencrypt-win-simple\httpsacme-v01.api.letsencrypt.org\exammple.com-crt.der
 Saving Issuer Certificate to C:\Users\Administrator\AppData\Roaming\letsencrypt-win-simple\httpsacme-v01.api.letsencrypt.org\ca-0A01414212341313A3D85736A0B85ECA708-crt.pem
 Saving Certificate to C:\Users\Administrator\AppData\Roaming\letsencrypt-win-simple\httpsacme-v01.api.letsencrypt.org\exammple.com-all.pfx
 Opened Certificate Store "My" 
 Adding Certificate to Store
 Closing Certificate Store WARNING: Unable to configure server software.
 Opened Certificate Store "My"
 Removing Certificate from Store exammple.com 2016/11/10 1:53:12下午
 Closing Certificate Store

中間會問幾個問題，原則上都 yes 即可，但是有一個動作是，自動更新時要用哪個帳號，如果要維持既有的，就回答 no 即可

參考如下，設定的檔案名稱及存放位置請參考步驟 2 的訊息!

<VirtualHost *:443>
    ServerAdmin admin@example.com
    ServerName www.example.com
    ServerAlias example.com
    
    SSLEngine on
    SSLCertificateFile "C:/Users/administrator/AppData/Roaming/letsencrypt-win-simple/httpsacme-v01.api.letsencrypt.org/example.com-crt.pem"
    SSLCertificateKeyFile "C:/Users/administrator/AppData/Roaming/letsencrypt-win-simple/httpsacme-v01.api.letsencrypt.org/example.com-key.pem"
    SSLCertificateChainFile "C:/Users/administrator/AppData/Roaming/letsencrypt-win-simple/httpsacme-v01.api.letsencrypt.org/ca-0A01414212341313A3D85736A0B85ECA708-crt.pem"
</VirtualHost>

憑證申請好之後每三個月需要更新一次。基本上會自動幫你更新，或是你也可以手動更新

letsencrypt.exe --renew