Ping is a tool that sends ICMP “echo request” packets to the host you specify. In this case the packets will be sent from this server to the host you specify in the ping form. Once the packets reach the host specified they should return to this server, bringing with them some detailed information about their journey.
Checking to see if a host is online - The host should respond to the ICMP "echo request" by returning our packets, indicating that it is online. However some hosts are configured not to accept ICMP traffic, so this is not definite answer.
Testing network speed - Ping will show the time it took for the packets to make a round trip between this server and the host you specify. Normal ping times should range anywhere between 30 to 150 milliseconds (ms). If ping shows that it took 400 ms to reach the host and return, then this may indicate that the network is stressed or that there may be a another type of network issue. Once again this is not always definite, some routers de prioritize ICMP traffic.
Checking for packet loss - Ping will send multiple packets, if some of them do not return then that indicates packet loss. networks can experience packet loss when the transmission medium is damaged (cables, network cards, fiber optics). Packet loss can also indicate port saturation or other types of network stress as well.