Remote computer open ports scan

Hi all,

My computer is connected to Wi-Fi router, then Wi-Fi router is connected to ADSL router which from internet provider obtains public IP.

When I scan that public IP from online sites there are three open ports:

21 ftp

23 telnet

80 http

I can telnet or open http session to ADSL router with that public IP. But what about ftp port?

If 21 ftp port is open can anybody scan computer hdd?

If yes with which tool?

How to close that open ports? Windows firewall, antivirus or Wi-Fi / ADSL router? Which is better?

Thanks