First, you need to backup the theme by:
1. Log in to blogger.com
2. Select the blog.
3. Click Theme then on the top right, click Backup/Restore.
4. Click Download theme.
5. Send the downloaded theme to you (via email or whatever)
Once another person received the theme, he/she can upload the file to his/her blog by:
1. Log in to blogger.com
2. Select the blog.
3. Click Theme then on the top right, click Backup/Restore.
4. Choose the file and click upload.