To download the client you will have to go to the GitHub website:
Over here you will face roughly this layout:
To actually download the client, click on the green button "Clone or download" (as indicated on the picture above).
A small window will appear, choose "Download ZIP" to start the download.
Once you've downloaded the ZIP file open it with your preferred program. The content should look similar to the picture below.
Unpack/Extract/Drag the whole map to a preferred location on your computer.
From this point the client is basically installed and ready to use.
The inside of the "otclientv8-master" folder should look like this (v1.7):
Before we can start playing Tibia we need to put the right sources in the right places.
First you need to download the right Tibia version, this can be done through various different sources such as Otservlist.org
Once you've downloaded the right Tibia version create a map called the version name in ...\otclientv8-master\data\things then drag the tibia.dat and tibia.spr file into the newly created folder.
Once the client is installed and the right Tibia client is placed in the correct folder location, it is time to run it. You can do this by clicking either "otclient_dx" or "otclient_gl". Both have exactly the same functionalities but one uses DirectX for the graphics and the other uses OpenGL.
Once you have opened the OTClientV8 the screen should look something like this (v1.7):
The following screen is the login screen. This is where you connect to the server and start playing. It's pretty straight forward you enter your login details of your account and specify the ip and port of the server (PS don't forget to choose the correct tibia version). The ip and port has to be written in the format IP:PORT as in the example above megatibia.com:7171.
When logged in the Client should look like this:
In the top right of the client you see a small robot head. That's the included otclientv8 bot. Read more about that here.