How to scan for open ports?

To scan for open ports on a target machine, you can use Nmap. Here are some basic commands:

Scan the most common 1000 ports on localhost:
```
nmap localhost
```
Scan all 65535 ports:
```
nmap -p- localhost
```
Scan a specific range of ports (e.g., ports 1 to 1000):
```
nmap -p 1-1000 localhost
```
Scan a specific IP address: Replace <YOUR_IP> with the target IP address.
```
nmap <YOUR_IP>
```

These commands will provide you with a list of open, closed, and filtered ports along with the services running on those ports.