1) Download and Install .NET Framework 4.8 if you're using Windows 7, 8 and above, should do this automatically for you.
2) Extract the files to a safe location on your computer.. If you lose files, you may lose access to your Steam account.
3) Run Steam Desktop Authenticator.exe and click the button to set up a new account.
4) Sign in to Steam and follow the setup instructions. Note: you still need a mobile phone that can receive SMS.
5) You may be asked to set up encryption, this is to make sure if someone gains access to your computer they can't steal your Steam account from this program. This is optional but highly recommended.
6) Select your account from the list to view the current login code, and click Trade Confirmations to see pending trade confirmations.
7) For your safety, remember to get Steam Guard backup codes! Follow this link and click "Get Backup Codes," then print out that page and save it in a safe place. You can use these codes if you lose access to your authenticator.
REMEMBER: Always make backups of your maFiles directory! If you lose your encryption key or delete maFiles by accident AND you didn't save your revocation code, you are screwed.
IF you lost your maFiles OR lost your encryption key, go here and click "Remove Authenticator" then enter your revocation code that you wrote down when you first added your account to SDA.
If you did not follow the directions and did not write your revocation code down, you're well and truly screwed. The only option is beg to Steam Support and say you lost your mobile authenticator and the revocation code.
How to use Steam Desktop Authenticator?
How to setup a Steam Guard Authenticator?
1) First you must to click "Setup New Account" button, then enter your username and password into the program window and click the "Login" button.
2) At the second stage, you must log in to your mail and receive the steam authorization code, then enter the code in the program field and click the "Accept" button.
3) Then you need to enter your mobile phone number in the program field and click the "Accept" button.
Next you will need to confirm your phone number using your email. Open the received letter and click on the "ADD PHONE NUMBER" button.
Remember! Only after confirming the phone, you can press the "OK" button, or you will have to do the installation again.
5) Next, you will be prompted to encrypt your program using a passkey. This is necessary in order to protect your accounts from intruders. You can cancel protection by clicking on the "Cancel" button.
6) Important! In the next step, you will need to write down the "R*****" recovery code. This code will be required to restore your account if you lose access to your program.
Please note that this code is also required for the final installation of your account.
7) Next, you should receive an SMS message to your mobile phone with the code sent by Steam. Enter this code in the program field and click the "Accept" button.
8) In the final step, you will need to enter the "R*****" recovery code that you wrote down earlier. Press the "Accept" button. Upon successful creation of the authenticator, you will be told that the authenticator is successfully linked.
Using SDA on multiple computers
You can use SDA on multiple computers at the same time, with the same Steam account(s).
To retain all Steam accounts from one computer, copy the entire folder where you have Steam Desktop Authenticator installed and move it to another computer using something like a flash drive or a network file transfer.
If you already have other accounts setup on a different computer, you can use File -> Import maFile to import single accounts to other computers.