How to find which ports are open or closed on my local pc?

You can find this out by installing nmap + running it against your IP.

nmap -sV -Pn $IP

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Since you're using Windows, you'll have to search for how to build nmap.

Or if you have a Linux or Mac machine running inside your LAN, nmap will be far easier to build/install on a UNIX-ish machine.

Example scan...

imac> sudo nmap -sV -Pn davidfavor.com
Password:
Starting Nmap 7.70 ( https://nmap.org ) at 2018-10-20 10:39 CDT
Nmap scan report for davidfavor.com (144.217.34.8)
Host is up (0.051s latency).
rDNS record for 144.217.34.8: ip8.ip-144-217-34.net
Not shown: 996 closed ports
PORT    STATE    SERVICE      VERSION
22/tcp  open     ssh          OpenSSH 7.5p1 Ubuntu 10ubuntu0.1 (Ubuntu Linux; protocol 2.0)
80/tcp  open     http         Apache httpd 2.4.33 ((Ubuntu))
443/tcp open     ssl/ssl      Apache httpd (SSL-only mode)
445/tcp filtered microsoft-ds
Service Info: OS: Linux; CPE: cpe:/o:linux:linux_kernel

Service detection performed. Please report any incorrect results at https://nmap.org/submit/ .
Nmap done: 1 IP address (1 host up) scanned in 15.80 seconds

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Go to GRC.com  and run the Shield's up app - IT will show you exactly what you are looking for

Go to GRC.com  and run the Shield's up app - IT will show you exactly what you are looking for

No, it won't actually. That tests your Router/Firewall - it doesn't give you an accurate report of what computer ports may be open and listening. That's incorrect advice for this question.

Thanks for your help!