how to install unsigned android application on the device?

Question

Currently a team of developers is working on Android application and during the development process testers already have to test the current state and report issues.

So

Answer 1

You can allow untrusted applications in the settings.

Settings / Applications / Unknown sources

with that setting on, you can just point your phone to the url of an .apk and install it IIRC.

It is also possible to install apks using debug mode and adb-commands over USB-cable.