First of all, you have to define encrypt/decrypt key pair for people you want to exchange secure message on keys management page.
Assuming your mobile no. is 098zzzzzzz and you want to exchange secure message with a contact whose mobile is 0935xxxxxx
1. Click on the keys mgt. from menu page
2. Type in this person's mobile no. in Contact mobile file
3. Random type in a string used for encryption key for your outgoing message to this contact on "Encryption key" field
4. Type in the decrypt string given by this contact (refer explanations in next step) which will be used to decode message from him/her on the "Decrypt key" field
On your counterpart's phone (contact people with the mobile no. 0935xxxxxx mentioned in earlier steps), repeat the same procedures for keys exchange definition as below
As you can see, he/she define your mobile (098zzzzzzz) in his/her keys mgt. page where
a. Key value defined in this contact's "Encryption key" field is the same value as you entered in your "Decrypt key" field (refer above screen)
b. Key value defined in this contact's "Decrypt key" field is the same value as you entered in your "Encrypt key" field (refer above screen)
Don't forget to click on the "Add xxx" or "Update xxx" button to save the keys definition for later use after finished keys definition.
Once done, either one can send secure message to his/her counterpart using the "send" function on main screen.
Shortly after, the targeted recipient will get a notification on his/her phone's status bar
Slide down the notification page, you will see a message from Secure SMS.
He/she can click on the notification to view the decrypted encrypted message from sender immediately.
Note for message with incorrect decrypt key defined, you will only see original encrypted message instead as demonstrated in message ID 1.
1. assistant sending confidential or classified information to boss
2. lovers exchange messages and want to keep those messages confidential inside the two only
3. bank / portal send one time OTA password to clients enhance security
4. business partners exchange confidential information or price quote
... and lots more we believe your will have your own creative way of using it. 
Well, that's basically all of what you need to get started. Have fun and hope you like our work.
Please don't hesitate to rate it as 5-star for our application in Android Market at https://market.android.com/details?id=com.ngnlive.plmn.securesms and "like" it on our Facebook fans' page at http://goo.gl/Dwm5S.
A big thanks to you in advance!
