Security levels and zones for use on a firewall are concepts that you create to structure your security requirements. Those concepts are then implemented by firewall rules.
Blocking traffic means can't access that server? ... When you do filtering with ACL on network device then it means you won't get any pings from the filtered addresses.
When you filter (block) some kind of traffic then that traffic doesn't reach its destination. For instance, you may widely permit http traffic to a web server but filter management traffic from all but one security zone, the one your administrator workstations are located in.
When you do filtering with ACL on network device then it means you won't get any pings from the filtered addresses. So it means literally you wouldn't get anything from that side like you wouldn't open the server page or wouldn't get any items from ftp servers.
Not quite. ACLs can be used on IP addresses (L3) but they may also be used on specific IP protocols or on the transport layer (L4), ie. port numbers. That way, you could e.g. permit ICMP echo (ping) for troubleshooting and filter other, potentially harmful ICMP traffic. For a public web server, you'd permit HTTP/HTTPS but filter FTP when it's only used administratively. Or permit FTP for an FTP server but filter HTTPS for the admin web interface.
The point is that you use firewall rules or ACLs to restrict the traffic to what exactly is required, nothing else. Security zones allow you easier categorization of sources and destinations, e.g. distinguish users from the open Internet, users from your LAN, admins from your LAN, public servers, and servers limited to LAN usage.