How to secure WiFi effectively? (Windows and Android)

[damien76]

Hi,

There are a lot of experts here so I opted to ask,

1. How to secure WiFi effectively?

2. How can I monitor my WiFi properly? I wanna know who is using my WiFi without my knowledge...(software apps, preferably free -- do not have money)

3. How can I boot them out or force disconnect them? (perhaps a How-To guide)

4. How can I bar them permanently from using my WiFi? (-- software apps perhaps)

My ISP isn't helping me and recently I discovered that this ISP has connected a "new" line to my supposedly solo line. The techs who did that I filed a complaint. 

Also how can I effectively monitor the WiFi connection, via Windows and Android?

I see in the net that in android, root is required If there be something I can use without root?

My brother is the subscriber so I do not have access to his pc but can I at least monitor our WiFi? 

Or if I can disconnect those people who piggy-back on our connection please help. 

Thanks!