Note: This short tutorial especially for windows users only and applicable with Windows PC. For Mac users you can install .deb file using Cyberduck ( instead of WinSCP.

1. Install OpenSSH on your iPhone via Cydia. Launch Cydia > Select “Sections” at haptic menu > Select “Networking” category > and select “OpenSSH” or you can tap “Search” in Cydia and type “OpenSSH” > Select “install” button at the right top and confirm it to install.

2. Download WinSCP software here and install it on your PC.

3. Enable SSH on your iPhone via SBSettings: (It is also possible to enable SSH via BossPrefs!) If you don't have the Toggle: Open SBSettings --> More --> Set Toggles and Enable the SSH Toggle. If you not clear about mentioned above, checkout my post on how to install SBSettings.

4. Launch WinSCP and click "New".

Host Name: Wi-Fi IP Address (check via SBSettings)
Port: 22
user name: root
password: alpine (Change this default password to prevent from hacker intruders and virus attack. Check out my post here on how to secure and change your default password)
File protocol: SCP (It's important to choose SCP unless you won't be able to open Terminal).

5. Click on "Login". The connection to your iPhone should be established. On the left you'll see the content of your PC and on the right the content of your iPhone:

6. Navigate to "/" on your iPhone by clicking on the dots (...)
Note: You should only see "/" in the red circle.

7. Go to /tmp/ folder and place the .deb file which you want to install there. For example, it's "stack.deb". Simply drag the file to the tmp folder.
NOTE: in this case i just used the stack.deb file as an example. This method can be used with any deb file!

8. We've got the deb file on our iPhone/iPod and now we only need to install the file. To do this press CTRL+T, Terminal should open:

9. Enter Command: dpkg -i /tmp/stack.deb and press enter. The deb file is being installed.

10. Remove the deb file from the /tmp/ folder.

11. Reboot and Respring your iPhone/iPod.

If you don't want to install the deb file via the WinSCP terminal you can also install it by using MobileTerminal on your iphone.

Search for "MobileTerminal" in cydia and install it. Follow steps 1-7 from above and then continue with these steps:

8. Start MobileTerminal
9. enter: su
10. enter: alpine
11. type dpkg -i /tmp/stack.deb
12. delete the deb file
13. reboot/respring

Alternate Ways To Install .deb file
Ssh your iPhone and make a folder called AutoInstall in/var/root/Media/Cydia/ so you have /var/root/Media/Cydia/AutoInstall which is case sensitive and drop this debs file in the autoinstall folder, respring and reboot your iPhone.