BetterCAP is a powerful, flexible and portable tool created to perform various types of MITM attacks against a network, manipulate HTTP, HTTPS and TCP traffic in real time, sniff for credentials and much more.
This is quite a generic description, mostly because if we’re talking about network MITM attacks, the logic and details heavily rely on the technique being used.
However, we can simplify the concept with an example. When you connect to some network, the router or switch is responsible for forwarding all of your packets to the correct destination, during a MITM attack we “force” the network to consider our device as the router.

Once this happens, all of the network traffic goes through your computer instead of the legit router or switch and at that point you can do pretty much everything you want, from just sniffing for specific data to actively intercepting and proxying all the requests of some specific protocol in order to modify them on the fly.
BetterCap is responsible for giving the security researcher everything he needs in one single tool which simply works, on GNU or Linux, Mac OS X, and OpenBSD systems.

Install Bettercap on Kali (Windows 10)

To install Bettercap run the following actions:
Install dependencies by running the following command from Kali console:
sudo apt-get install build-essential ruby-dev libpcap-dev

Install Bettercap with the following command:
sudo apt-get update
sudo apt-get install bettercap
sudo apt-get install openssl
Bettercap might not work out of the box and you might need to reinstall by performing the following:
apt-get install ruby-dev
gem uninstall eventmachine
gem install eventmachine
Note: If you are facing issues with the stable release of Bettercap, you can also install the development release using the following:
git clone https://github.com/evilsocket/bettercap
cd bettercap
bundle install
gem build bettercap.gemspec
sudo gem install bettercap*.gem